This PR is part of #4767. It
1. adds the ability to follow a local person from a distant federation server (see tests/integration/api_activitypub_person_inbox_follow_test.go)
2. streamlines the router code (refactor the person conversion & handling of inbox requests in service direction, unifies service call signature & error handling)
3. introduces queues for decoupling outgoing communication (delivery retry to cope network issues or distant service downtimes) and
4. adds minor fixes to integration tests (test timeout & invalid inbox activities)
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/8720
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Michael Jerger <michael.jerger@meissa-gmbh.de>
Co-committed-by: Michael Jerger <michael.jerger@meissa-gmbh.de>
