Refactor /publish to use a designated service entrypoint rather than queue a worker

The following discussion from !30906 (merged) should be addressed:

• @splattael started a discussion:

  Non-blocking: Here, we are circumventing TriggerPublishService which should act as main point of kicking off publishing incidents. Personally, I think the worker is an implementation detail and should be hidden from the outside.

  Having said that, this change allows us to mark issues via /publish in notes, so it's a good iteration 👍

  I'll open a follow-up issue which will suggest to use TriggerPublishService instead.

Problem

Trigger a publish via a note /publish via StatusPage::TriggerPublishService.

Proposed solution

We could soften the restrictions in StatusPage::TriggerPublishService#eligable_issue_id_from_note to achieve this but this needs investigation.