Added this because recently, there have been more problems with `docker-compose build` where it errors:
ERROR: Service 'server' failed to build: failed to parse platform : "" is an invalid component of "": platform specifier component must match "^[A-Za-z0-9_-]+$": invalid argument
Recent Docker versions have switched to using `buildx` (BuildKit) to build containers, but that needs to be enabled, either in `daemon.json` or through an environment variable. But since we are using Docker Compose, it doesn't pass it to Docker; so the environment variable needs to be set. At least that's what I've heard and figured out sweat_smile My explanation might be very wrong - but it works :)
This should fix most scaling problems without needing to start
more server instances. By default, waitress maintains at most
4 threads. This works fine if the database is small (sub 100k posts)
but causes a large Task queue depth to occur if the database is larger.
Letting users increase the amount of threads means that one server instance
is able to handle more requests without locking up the rest of the site.
This adds a new environment variable to .env, THREADS, which can be used to
configure the amount of threads to start and is by default set to 4
(the default amount used by waitress).
