add cloudwatch dashboard

[ccbrown]

What It Does

Adds a CloudWatch dashboard to the CDK deployment.

Related Issues

• Built-in observability #28

[Copilot]

Pull Request Overview

This PR adds a CloudWatch dashboard to the CDK deployment for enhanced observability.

• Introduces new properties (allRegions and envSlug) in global-apex-stack.ts and environment.ts to support multi-region metrics.
• Adds a custom Dashboard construct to create several GraphWidgets for API requests, API errors, Lambda invocations, maximum Lambda duration, and SQS oldest message age.
• Updates documentation in README.md to reflect the new observability features.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
aws/lib/global-apex-stack.ts	Added Dashboard construct with multi-region CloudWatch metrics.
aws/lib/environment.ts	Updated GlobalApexStack initialization to pass new dashboard props.
aws/README.md	Added Observability section describing the new CloudWatch dashboard.

Comments suppressed due to low confidence (2)

aws/lib/global-apex-stack.ts:87

• The metric label for API Errors uses only the region name which may cause ambiguity between 4xx and 5xx error metrics. Consider appending the metric type (e.g., ${region}-${metric}) to the label for clearer identification.

for (const metric of ['4xx', '5xx']) {

aws/lib/global-apex-stack.ts:49

• [nitpick] Naming the Construct as 'Dashboard' could be confusing since it shares the same name as the CloudWatch Dashboard object. Consider renaming the construct (e.g., 'CloudWatchDashboard') to differentiate it.

const dashboard = new cw.Dashboard(this, 'Dashboard', {