updates for default azure credential and azure identity package

[manvkaur]

This pull request updates the Azure identity dependencies and standardizes the way Azure token credentials are set and used across the codebase. The main focus is on ensuring that the AZURE_TOKEN_CREDENTIALS environment variable is set appropriately for different build environments (development vs. production), and that the correct overload of DefaultAzureCredential is used. These changes improve consistency and reliability in how Azure credentials are managed.

Dependency version updates:

• Upgraded the Azure.Identity dependency in both samples/assistant/java/pom.xml (from 1.16.2 to 1.18.0) and src/WebJobs.Extensions.OpenAI/WebJobs.Extensions.OpenAI.csproj (from 1.13.2 to 1.17.1) for improved security and compatibility. [1] [2]

Environment variable handling for credentials:

• Added logic in constructors of AzureAISearchProvider, CosmosDBNoSqlSearchProvider, and OpenAIClientFactory to set the AZURE_TOKEN_CREDENTIALS environment variable to 'prod' in release builds and 'dev' in non-release builds if it is not already set. This ensures the correct environment is used for authentication. [1] [2] [3]

Credential instantiation consistency:

• Updated instantiations of DefaultAzureCredential in all relevant providers and client factories to use the DefaultEnvironmentVariableName overload, aligning with the new environment variable logic and ensuring consistent credential sourcing. [1] [2] [3]