fix: Add Cosmos DB Account Key Output for Environment Configuration

[Prasanjeet-Microsoft]

Purpose

• To include the missing AZURE_COSMOSDB_ACCOUNT_KEY output in the Bicep template, ensuring it is available in the generated .env file for proper local application execution and authentication when using Cosmos DB with AZURE_AUTH_TYPE=keys

Does this introduce a breaking change?

• Yes
• No

How to Test

• Get the code

git clone [repo-address]
cd [repo-name]
git checkout [branch-name]
npm install

What to Check

Verify that the following are valid:

• Run azd up and verify the .env file includes the AZURE_COSMOSDB_ACCOUNT_KEY with a valid value.
• Confirm the application correctly reads this variable and can authenticate against Cosmos DB.
• Ensure no disruption or breaking changes to existing deployments or environment setups.
• Validate local development and debugging work as expected with the updated environment variables