Azure: Support for Azure Active directory Override

[npapapietro]

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

• Add active_directory_endpoint configuration for overriding the Microsoft Entra ID authority host, enabling authentication in sovereign environments such as Azure US Secret Cloud.
• Add explicit workload identity authentication with use_workload_identity.
• Ensure workload identity and client-secret authentication are mutually exclusive.
• Preserve the existing authentication behavior when the new options are not configured.
• Document the new Azure configuration options and add validation and credential tests.

Verification

• Ran go test ./providers/azure.
• Verified that existing Azure provider tests continue to pass.
• Added tests covering workload identity configuration, mutually exclusive client-secret authentication, and custom authority endpoint handling.
• Ran make docs to update the generated Azure configuration documentation.