fine grade control about retention policy

[Mai-Lapyst]

Pitch

The idea is to expand the retention policy setting, which currently only consists out of media files and all other content, and splitting it to multiple settings so admins have a much more fine graded controll about what to hold on to and what to delete when.

I'll favor for introducing the following new settings:

• retention period for all accounts that users of the local instance follow
• retention period for DM's (with maybe the possibility to set it to infinite)
• retention period for bot accounts
• retention poriod for everything other

Also one more extension to that would be to add an interaction counter as suggessted in https://github.com/mastodon/mastodon/discussions/19260 (but never followed up upon) so boosts, favs and bookmarks keep all other content where no-one follows the author longer. Which eiter can be grouped together or split into singular values to allow for even more controll.

Motivation

My motivation behind this is to allow folks to keep the most usefull data while better discarding data that isn't of much relevance while giving instance admins the controll to decided what actually is importand to them and/or their users.

It would also benefit people in very different ways:

• folks that write a bunch of DM's can hold longer onto them
• boosts and the imo even more vital bookmarks get to stay longer onto your instance which benefits people that maybe use the bookmark system to "save" posts of great value
• benefits admins that decide that bot accounts should be viewable but dont want the execcive data that some remote-bot might allocate over time on their instance. And for any user that want the data anyway, prioritising the retention setting for follows above bots could help here as well

[Mai-Lapyst]

I'm also willing to help implementing this and/or makeing a proof of concept if needed.