Blacklist URLs and words in posts #90

Urls shorteners are often used by spammers and functionally useless in 2024. Extend the codebase to automatically block all messages from known services.
Possible sources:

Maybe it can be implemented by loading the list at runtime (can php cache the file?), or by encoding it in the php source.

The issue right now is: where to store all the urls?
Do we reaload everything from a file upon each request?
Do we use the DB as a storage?
Do we cache anything?

The syntesis would be to store most of the data in the DB, in order to allow the staff to edit it, while also providing a tool to automatically import a file into the db.

This syntesis can also be made generic over any word, allowing for more varied filtering.

Such a feature could allow to singlehandedly obsolete most of the event system current usage over instance-config.php

Who inserted what in the list should be tracked, with the entries inserted by tool marked as such.
This can allow the insertion of multiple lists which can then be removed by simply removing all the entries inserted by someone.

The matching itself should be done with regexes, with a possible UI setting to enable case-sensibility.

Since regexes can potentially be very broken, we should start by only allowing plaintext filtering.
This would require escaping regex symbols upon insertion of new entries

This could potentially be hooked up with the system described in #78