Alpine 3.17 has jemalloc back in it's repositories, which means it can just
be installed through the package manager.
Also explicitly install postgres 12 packages. That was already possible with
alpine 3.16 but I didn't know about it back then.
2.7.3 has been used in prod since the start of april, so the repo
should reflect the change.
To those wondering how to implement this change in prod:
update the target system packages to latest versions
`ruby-instally ruby 2.7.3` either as the target user or system wide
`bundle install` from inside repo to install required gems
ensure that everything works with `bundle exec rails c`
restart the service when convenient
