BED-4931: Add Audit Logging for SAML Authentication Attempts

[iustinum]

Description

This PR resolves an issue where successful SAML provider logins were not generating LoginAttempt entries in the /api/v2/audit endpoint, despite being logged in the Elastic logs.

Motivation and Context

This change addresses BED-4931.

For secret-based authentication, audit logging is handled within the authenticator.LoginWithSecret() method via auditLogin(), which creates LoginAttempt entries visible in the /api/v2/audit response body. However, in the SAML authentication flow, login attempts were not being audited, as the handler for the /api/v1/login/saml/{saml_provider_name} endpoint did not create equivalent audit log entries.

This PR resolves the issue by introducing audit logging in the SAML authentication handler and ensuring that all login attempts, including those using SAML, are properly logged in the audit trail.

The solution aligns with the existing audit logging pattern and provides a consistent and complete audit trail for SAML authentication attempts.

How Has This Been Tested?

The changes were tested by extending the existing test cases for the SAML login handler. A mock for CreateAuditLog was added to verify that audit log entries are created as expected. The mocking expectations were also updated to reflect the new code flow, including logging for both successful authentication attempts and failures.

Screenshots (optional):

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• I have met the contributing prerequisites
  • Assigned myself to this PR
  • Added the appropriate labels
  • Associated an issue: Issues and Pull Requests README #672
  • Read the Contributing guide: https://github.com/SpecterOps/BloodHound/wiki/Contributing
• I have ensured that related documentation is up-to-date
  • Open API docs
  • Code comments (GoDocs / JSDocs)
• I have followed proper test practices
  • Added/updated tests to cover my changes
  • All new and existing tests passed