docs: Add explicit User-Assigned Managed Identity (UAMI) example for Cosmos DB binding

[paulyuk]

Summary

This PR adds a clearer example showing how to configure Cosmos DB connections using a User-Assigned Managed Identity (UAMI) with explicit app settings.

Problem

The existing documentation mentions credential and clientId properties for user-assigned managed identities but lacks a concrete JSON example.

Solution

Added a new "User-assigned managed identity" subsection with:

• A table showing the three required properties (accountEndpoint, credential, clientId)
• A complete JSON example developers can copy directly
• A tip explaining when UAMI is recommended

Changes

• includes/functions-cosmosdb-connections.md: Added UAMI configuration example

Related

• Event Hubs PR: docs: Add explicit User-Assigned Managed Identity (UAMI) example for Event Hubs binding #128219
• Service Bus PR: docs: Add explicit User-Assigned Managed Identity (UAMI) example for Service Bus binding #128220
• Tracking issue: [Documentation] Align MS Learn Azure Functions docs with Copilot skill recipes microsoft/GitHub-Copilot-for-Azure#973

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PRMerger Results

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[Copilot]

Pull request overview

This PR adds explicit documentation for configuring Azure Cosmos DB connections using User-Assigned Managed Identity (UAMI) in Azure Functions. The existing documentation mentioned the credential and clientId properties but lacked a concrete example that developers could directly reference and copy.

Changes:

• Added a dedicated "User-assigned managed identity" subsection with property details, complete JSON configuration example, and best practice guidance

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[ttorble]

@mattchenderson

Can you review the proposed changes?

IMPORTANT: When the changes are ready for publication, adding a #sign-off comment is the best way to signal that the PR is ready for the review team to merge.

#label:"aq-pr-triaged"
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