The pgbouncer build is currently broken because of a missing build
dependency. This went unnoticed because the build script previously
didn't report any build errors.
Fix the build by installing the missing libevent-dev dependency.
Ruby 2.7.1 is only available on Debian Buster, so we have to upgrade
from Debian Stretch.
Fix install-essentials for Debian 10 (Buster):
1. MySQL client is no longer needed
2. Yank libgdbm3 and libgdbm-dev because it's not clear why it's needed
3. Pull legacy nodejs from Debian Buster builds since Node 12.x conflicted
Every package manager should clean up after themselves in order to keep
docker layers neat and tiny:
apt (Debian/Ubuntu package manager):
- unneeded dependencies are cleared (autoremove)
- caches are cleaned (clean)
- package lists are deleted
yum (CentOS package manager),
zypper (OpenSuse package manager)
- should clear caches after installing dependencies
pip (Python package manager),
apk (Alpine package manager)
- should use no cache for installing dependencies
