Some formatting changes for showing auth provider config guidance

Summary:
Ref T7667. On the road to locking the auth config, also clean up some minor UI issues:

• Only show the warning about not Phacility instance auth if the user isn't a manager (see next diff).
• When rendering more than one warning in the guidance, add bullets.
• I didn't like the text in the auth.config-lock config setting.

Test Plan: Loaded the page, saw more reasonable-looking guidance:

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T7667

Differential Revision: https://secure.phabricator.com/D20400