chore: Enhance LDAP authentication logging

[luohoufu]

What does this PR do

This pull request includes changes to improve logging and simplify the iteration over realms in the authentication and authorization processes. The most important changes include adding debug logging for empty LDAP groups and using the realm type instead of the index for logging in the Authenticate and Authorize functions.

Improvements to logging:

• modules/security/realm/authc/ldap/ldap.go: Added debug logging for cases where the LDAP groups are empty in the mapLDAPRoles function.

Codebase simplification:

• modules/security/realm/realm.go: Replaced the index variable with the realm type in debug logging for the Authenticate function.
• modules/security/realm/realm.go: Replaced the index variable with the realm type in debug logging for the Authorize function.

Rationale for this change

Standards checklist

• The PR title is descriptive
• The commit messages are semantic
• Necessary tests are added
• Updated the release notes
• Necessary documents have been added if this is a new feature
• Performance tests checked, no obvious performance degradation