switch to s3 for serving user uploads

https://whitenoise.readthedocs.io/en/latest/django.html#serving-media-files suggests serving user-uploaded assets from same domain as app is problematic and i think i agree

plus i don't really want to fuss w nginx stuff anymore

so we should just use cloudflare r2 instead in prod (s3 compatible and robosub and comet robotics already use cloudflare for other stuff)

then for local just use local file storage to make dev set up easier

could be worth investigating whether to use whitenoise for serving club manager's actually static assets - would mean dropping nginx which means one less service to maintain

this wouldn't be that problematic - we don't really depend on it for ssl termination since both clubs use cloudflare tunnel. so at the end of the day cloudflare is functioning as protection/reverse proxy anyway. don't really need nginx at all