Different search backends, in particular meilisearch as an additional one
The MR introduces a way to have different search backends and implements a way for them to easily index and remove posts from index when they are deleted. Meilisearch seems to work fairly well, and doesn't consume too much resources seemingly. It's certainly more accurate than the built-in postgres search. In the future, additional backends may be added, if somebody wants to. The obvious one would be elasticsearch, but I really would rather not work out how that one works for now.
The MR includes some simple tests and an extension to documentation, concerning the search configuration. Don't know if any additional documentation or description is necessary, but there seems to be more places to put documentation into, so just tell me if I have to add it to more places.
I've been running this for about a month and it seems to work fairly well, the slowest part is going to the database to fetch full posts, since the search index only stores some basic stripped info to save space.
This is also connected in some part to pleroma-fe!1410, actually making the search even more useful.
On the frontend, no changes are actually required, and just swapping the search for the new one works, but the aforementioned MR allows to load more than 20 newest results.