Avatar Commend: Simplified and updated during review

Avatar Commend: Simplified and updated during review

During review of #4560.

- Simplified command to share as much log as possible across different
  run options.
- Extracted out user handling to share with MFA command.
- Added specific handling for disabled avatar fetching.
- Added mention of avatar endpoint, to make it clear where these avatars
  are coming from (Protect against user expectation of LDAP avatar sync).
- Simplified a range of the testing.
- Tweaked wording and code formatting.