This change converts existing CHECKS files into a healthchecks key that is understood by 'docker-container-healthchecker'. This tool supports a number of different types of container healthchecks - command, http, uptime - and can perform healthchecks against non-web processes.
The use of the old CHECKS file is now deprecated, and will be removed in the next minor version. Users can use the 'docker-container-healthchecker' to convert existing CHECKS files to the new format automatically.
Closes#2760
Recent Dokku changes invalidate a bunch of docs around where files need to be placed in order for Dokku to respect them. This doc change clarifies where files are extracted from in cases where source code is available, which should hopefully make users less confused about how the system works.
See https://railsnotes.xyz/blog/deploying-ruby-on-rails-with-dokku-redis-sidekiq-arm-docker-hetzner for the inspiration - I was reading through it and was like 'these docs are definitely incorrect...'.
This changes restarts to drop the 'release' part that currently gets triggered, which also helps reduce the possibility that a new image layer will be added due to predeploy deploy triggers.
Note that the old method essentially halfway-rebuilt the app (which was what added the extra layer). This refactor removes that, which is a bc-break.
Additionally, scaling processes will result in deploying _only_ restarting the processes being scaled.
Closes#2184
