Possibly solve synapse DB huge size issues caused by unreferenced state groups

[Gredin67]

Issue : database growing crazy when using mautrix bridges.

More information : https://wiki.chatons.org/doku.php/services/messagerie_instantanee/matrix#nettoyer_les_evenements_orphelins

Solution
clean unreferenced state groups.
Provide a build of https://github.com/erikjohnston/synapse-find-unreferenced-state-groups
in the yunohost package

[Josue-T]

Honestly I won't implement this on my side for theses reason:

• I have many other projects with higher priority
• It's a project from one of the maintainer of synapse but it still not official, and it's not a lot maintained, the last commit is ~2 year old.

But I'm still open for a Pull request if you want.

[hieronymousch]

I learned to not directly use the bridges on my primary matrix server and use an intermediate one just for bridges... that way my primary matrix server stays more 'clean'