Add support for global system tag events

[StefanRichterHuber]

Describe why it is important and where it will be useful

As of now, support for several file events were added, which are a great addition for automated workflows. Thank you!

To have a more fine-grained control, it would be useful to also be able to track all events around system tags (addition and removal). This way a user can assign a tag to a file or folder and trigger an external app. These system tags especially play well together with Nextcloud Flow, which allows to add tags on certain events.

E.g. All text files with system tag 'AI content' will automatically be added to a vector db.

Describe your proposed solution

There seems to be an group of events around \OCP\SystemTag which could be more-or-less directly added to the existing Events Listener api.

Describe alternatives you've considered, if relevant

Searching all user folders in an interval for files with the required tags, which induces unnecessary load on both the nextcloud server as well as the ex app.

Additional context

No response

[bigcat88]

we will add this soon, as also more options for file events (e.g., triggering only for specified users, custom path mask).

Thank you for your continued interest in this project, we really appreciate it.