docs: update auth .md file

[Shreyas-Microsoft]

Purpose

This pull request updates documentation to clarify environment variable usage and expand instructions for assigning Azure roles. The most important changes are grouped below:

Authentication Environment Variable Setup:

• Updated the example for enabling authentication by changing ENV ENABLE_AUTH=true to ENABLE_AUTH=true in docs/AddAuthentication.md, ensuring consistency and correctness in environment variable configuration.

Azure Role Assignment Instructions:

• Added a new example demonstrating how to assign the "Azure AI User" role using the Azure CLI in docs/LocalDevelopmentSetup.md, helping users set up the necessary permissions for Azure OpenAI resources.

Does this introduce a breaking change?

• Yes
• No

Golden Path Validation

• I have tested the primary workflows (the "golden path") to ensure they function correctly without errors.

Deployment Validation

• I have validated the deployment process successfully and all services are running as expected with this change.

What to Check

Verify that the following are valid

• ...

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