[#1668] Restricted access to app metrics endpoint by default. Added ability to configure IP whitelist for this endpoint.
Added tests and documentation.

[#3053] Removed target accessibility checks for OStatus endpoints delegating to RedirectController. Added tests.

Closes #2198

Bugfix: MRF and Pipeline Ingestion

See merge request pleroma/secteam/pleroma!15

[#2497] Media preview proxy: misc. improvements (`static` param support, dynamic fifo pipe path), refactoring.

Mastodon API: fix the public timeline returning an error when the `reply_visibility` parameter is set to `self` for an unauthenticated user

In practice, it was already removed half a year ago, but the description
 and cheatsheet entries were still there.

The migration intentionally does not use ConfigDB.get_by_params, since
this will break migration code as soon as we add a new field is added
 to ConfigDB.

Closes #2086

Also remove the example from the cheatsheet, there is no need for it
when the types are simple