Backend performance improvements about karrot-frontend

[nicksellen]

Sentry also seems to log slow SQL queries now, see https://karrot-dev.sentry.io/issues/?project=147126

[nicksellen]

I think I can call this resolved now, from various adjustments over the last few weeks:

• turning off on demand image creation for versatileimagefield
• switching to orjson json serializer
• unix socket connections for postgres and redis
• connection pooling for postgres
• psycopg upgrade claims some performance improvement

It would always be nice to be faster, /api/bootstrap/ is still too slow if you are part of many larger groups, so future improvements could still be:

• send less data for bootstrap endpoint
• perhaps more on-demand data fetching, less relying on having all the data in memory (groups, places, and users come to mind)
• also, can switch to SSDs on the server soon perhaps, which may or may not make a lot of different (as most stuff is in memory anyway)
• some query/index optimizing could make sense
• statistics endpoint is very slow, although probably OK for that use case
• available activities is a bit slow, as it does a more complex participant type query check