add debug auth report support

What does this MR do?

• *Adds support for writing out an authentication debug report to aid users in determining why a login attempt failed.

** Opt'd to make the flag truthy so we will always have deterministic name and location for the HTML report.

What are the relevant issue numbers?

#325006

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Job definition example
  • Vendored CI Templates (also in CE)
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer