feat(unreal): Add metrics documentation (#16285)

This PR adds documentation for the Sentry Metrics feature in the Unreal
Engine SDK.

Related to:
- getsentry/sentry-unreal#1214

Author: tustanivsky

docs/platforms/unreal/metrics/index.mdx

@@ -0,0 +1,34 @@
+---
+title: Set Up Metrics
+sidebar_title: Metrics
+description: "Metrics allow you to send, view and query counters, gauges and distributions from your Unreal Engine game to track application health and drill down into related traces, logs, and errors."
+sidebar_order: 5700
+beta: true
+---
+
+With Sentry Metrics, you can send counters, gauges, and distributions from your Unreal Engine game to Sentry. Once in Sentry, these metrics can be viewed alongside relevant errors, and searched using their individual attributes.
+
+<Alert>
+  This feature is currently in open beta. Features in beta are still in progress
+  and may have bugs.
+</Alert>
+
+## Requirements
+
+<PlatformContent includePath="metrics/requirements" />
+
+## Setup
+
+<PlatformContent includePath="metrics/setup" />
+
+## Usage
+
+<PlatformContent includePath="metrics/usage" />
+
+## Options
+
+<PlatformContent includePath="metrics/options" />
+
+## Default Attributes
+
+<PlatformContent includePath="metrics/default-attributes" />

docs/product/explore/metrics/getting-started/index.mdx

@@ -306,6 +306,14 @@ To set up Sentry Metrics, use the links below for supported SDKs. After it's bee
     url="/platforms/go/metrics/"
   />
 
+### Gaming
+
+- <LinkWithPlatformIcon
+    platform="unreal"
+    label="Unreal Engine"
+    url="/platforms/unreal/metrics/"
+  />
+
 ## Upcoming SDKs
 
 We're actively working on adding Metrics functionality to additional SDKs. Check out these GitHub issues for the latest updates:

platform-includes/metrics/default-attributes/unreal.mdx

@@ -0,0 +1,5 @@
+The Unreal Engine SDK automatically attaches the following attributes to every metric:
+
+<Include name="metrics/default-attributes/core" />
+
+<Include name="metrics/default-attributes/user" />

platform-includes/metrics/options/unreal.mdx

@@ -0,0 +1,42 @@
+The following configuration options are available for Sentry Metrics in Unreal Engine:
+
+| Option | Description | Default |
+|--------|-------------|---------|
+| **Enable Metrics** | Master toggle for the metrics feature | `false` |
+| **Before Metric Handler** | Handler to modify or filter metrics before sending | None |
+
+### Before-Metric Handler
+
+To filter metrics or modify them before they are sent to Sentry, create a custom before-metric handler class:
+
+```cpp
+UCLASS()
+class UCustomMetricFilter : public USentryBeforeMetricHandler
+{
+    GENERATED_BODY()
+public:
+    virtual USentryMetric* HandleBeforeMetric_Implementation(USentryMetric* Metric) override
+    {
+        // Drop metrics with specific names
+        if (Metric->GetName().Contains(TEXT("debug")))
+        {
+            return nullptr; // Return null to prevent sending
+        }
+
+        // Modify metric attributes
+        Metric->SetAttribute(TEXT("build"), FSentryVariant(TEXT("production")));
+
+        return Metric; // Return the metric to send it
+    }
+};
+```
+
+Configure the handler in project settings under **Hooks > Custom `beforeMetric` event handler**, or set it programmatically:
+
+```cpp
+SentrySubsystem->InitializeWithSettings(FConfigureSettingsNativeDelegate::CreateLambda([=](USentrySettings* Settings)
+{
+    Settings->EnableMetrics = true;
+    Settings->BeforeMetricHandler = UCustomMetricFilter::StaticClass();
+}));
+```

platform-includes/metrics/requirements/unreal.mdx

@@ -0,0 +1 @@
+Metrics for Unreal Engine are supported in Sentry Unreal Engine SDK version `1.7.0` and above.

platform-includes/metrics/setup/unreal.mdx

@@ -0,0 +1,24 @@
+To enable metrics in your Unreal Engine project, you need to configure the Sentry SDK with metrics enabled.
+
+### Project Settings Configuration
+
+1. Open your project settings: **Project Settings > Plugins > Sentry**
+2. Check the **Enable Metrics** option
+
+### Programmatic Configuration
+
+Alternatively, you can enable metrics programmatically when initializing the SDK:
+
+```cpp
+#include "SentrySubsystem.h"
+
+void ConfigureSentryWithMetrics()
+{
+    USentrySubsystem* SentrySubsystem = GEngine->GetEngineSubsystem<USentrySubsystem>();
+
+    SentrySubsystem->InitializeWithSettings(FConfigureSettingsNativeDelegate::CreateLambda([=](USentrySettings* Settings)
+    {
+        Settings->EnableMetrics = true;
+    }));
+}
+```

platform-includes/metrics/usage/unreal.mdx

@@ -0,0 +1,71 @@
+Once metrics are enabled, you can emit metrics using the Sentry subsystem.
+
+### Metric Types
+
+| Type           | Use For                                      |
+| -------------- | -------------------------------------------- |
+| `Counter`      | Events (orders, clicks, API calls)           |
+| `Gauge`        | Current values (queue depth, connections)    |
+| `Distribution` | Value ranges (response times, payload sizes)  |
+
+### Counters
+
+Track the number of times something happens:
+
+```cpp
+#include "SentrySubsystem.h"
+
+USentrySubsystem* SentrySubsystem = GEngine->GetEngineSubsystem<USentrySubsystem>();
+
+SentrySubsystem->AddCount(TEXT("api.requests"), 1);
+```
+
+### Gauges
+
+Track current values that can go up or down:
+
+```cpp
+SentrySubsystem->AddGauge(TEXT("active_connections"), 42, USentryUnitHelper::MakeSentryUnit(ESentryUnit::None));
+```
+
+### Distributions
+
+Track a range of values (e.g., response times):
+
+```cpp
+SentrySubsystem->AddDistribution(TEXT("response.time"), 150.5f, USentryUnitHelper::MakeSentryUnit(ESentryUnit::Millisecond));
+```
+
+### Custom Attributes
+
+Add attributes to filter and group metrics in Sentry:
+
+```cpp
+TMap<FString, FSentryVariant> Attributes;
+Attributes.Add(TEXT("endpoint"), FSentryVariant(TEXT("/api/orders")));
+Attributes.Add(TEXT("region"), FSentryVariant(TEXT("us-west")));
+
+SentrySubsystem->AddCountWithAttributes(TEXT("api.calls"), 1, Attributes);
+```
+
+All metric methods have a `WithAttributes` variant:
+- `AddCountWithAttributes()`
+- `AddDistributionWithAttributes()`
+- `AddGaugeWithAttributes()`
+
+### Units
+
+For gauge and distribution metrics, specify a unit to help Sentry display values in a human-readable format. The SDK provides the `ESentryUnit` enum with predefined units for duration, information, and fraction categories:
+
+```cpp
+// Using predefined units
+SentrySubsystem->AddGauge(TEXT("memory.usage"), 1024.0f, USentryUnitHelper::MakeSentryUnit(ESentryUnit::Byte));
+SentrySubsystem->AddDistribution(TEXT("latency"), 42.5f, USentryUnitHelper::MakeSentryUnit(ESentryUnit::Millisecond));
+
+// Using a custom unit
+SentrySubsystem->AddDistribution(TEXT("frame.rate"), 60.0f, USentryUnitHelper::MakeSentryCustomUnit(TEXT("fps")));
+```
+
+### Blueprint Support
+
+You can also emit metrics from Blueprints by calling the **Add Count**, **Add Distribution**, or **Add Gauge** nodes on the Sentry subsystem. Use the **Make Sentry Unit** node to specify measurement units.