feat: Restart the queue worker after cache clearing, ext enable/disable, save settings

[imorland]

**Fixes #3563 **

Changes proposed in this pull request:
Adds a subscriber to trigger the queue to restart after certain events

Reviewers should focus on:
Tested locally with a standard redis based queue. Doesn't work with blomstra/horizon, although I think there's a seperate issue with that extension, which I'll start to investigate now

Necessity

• Has the problem that is being solved here been clearly explained?
• If applicable, have various options for solving this problem been considered?
• For core PRs, does this need to be in core, or could it be in an extension?
• Are we willing to maintain this for years / potentially forever?

Confirmed

• Frontend changes: tested on a local Flarum installation.
• Backend changes: tests are green (run composer test).
• Core developer confirmed locally this works as intended.
• Tests have been added, or are not appropriate here.