Add healthcheck commands to docker-compose.yml

[BenLubar]

This will allow Docker to be automatically check the health of services.

Docker won't do anything other than showing the state in the output of docker-compose ps by default, but some management tools may watch for container health events.

Here's what my local instance looks like right now:

          Name                        Command                  State                     Ports
-------------------------------------------------------------------------------------------------------------
mastodon_db_1              docker-entrypoint.sh postgres    Up (healthy)
mastodon_es_1              /usr/local/bin/docker-entr ...   Up (healthy)
mastodon_redis_1           docker-entrypoint.sh redis ...   Up (healthy)
mastodon_redis_cache_1     docker-entrypoint.sh redis ...   Up (healthy)
mastodon_sidekiq_1         /sbin/tini -- bundle exec  ...   Up             3000/tcp, 4000/tcp
mastodon_streaming_1       /sbin/tini -- yarn start         Up (healthy)   3000/tcp, 127.0.0.1:4000->4000/tcp
mastodon_web_1             /sbin/tini -- bash -c rm - ...   Up (healthy)   127.0.0.1:3000->3000/tcp, 4000/tcp

[nightpool]

why should we specify these explicitly? shouldn't these be part of the postgres docker image?

[nightpool]

why was sidekiq excluded?

[Gargron]

@nightpool I don't know how you could check Sidekiq health from a script. It's not like it accepts connections...