support Azure managed identity

[gainskills]

Summary

We failed a security compliance check becasue current new relic implementation with password and service principle secret, this PR adds Azure Managed Identity authentication support for the nri-mssql integration, expanding the existing Azure AD Service Principal authentication capabilities.

Key Changes

• Features Added

• Managed Identity Support: New USE_MANAGED_IDENTITY configuration option enables authentication via Azure Managed Identity (system or user-assigned)

• Automatic encryption: Managed Identity authentication enforces encrypted connections (encrypt=true) by default, regardless of ENABLE_SSL setting

• Smart certificate handling: Defaults to TrustServerCertificate=true for Managed Identity to prevent SSPI channel binding errors with Azure SQL MI, unless a certificate is explicitly provided

Files Modified

• src/args/argument_list.go: Added UseManagedIdentity boolean flag
• src/connection/sql_connection.go:
  • Updated determineAuthMethod() to check for Managed Identity first (takes precedence)
  • Enhanced CreateAzureADConnectionURL() to support both Service Principal and Managed Identity auth methods
• src/connection/sql_connection_test.go: Added 5 new test cases covering various Managed Identity scenarios
• mssql-config.yml.sample: Updated documentation with clear examples for both authentication methods

Backward Compatibility

Fully backward compatible - existing Service Principal authentication remains unchanged

[CLAassistant]

All committers have signed the CLA.