Fix nginx caching issues
Nginx is currently not caching data because proxy_buffering needs to be enabled for caching to work at all, and we are receiving a Cache-Control header from Pleroma that states "max-age=0, private, must-revalidate"
Even disregarding the Cache-Control header that should actually be set to "public, max-age=1209600" as defined in the reverse_proxy code, we don't want to obey this header at all as it overrides our Nginx caching rules.
After making these changes you should see files created in /tmp/pleroma-media-cache/ as expected