Use systemd preset to configure services in pmaports

This is based on a ton of work from @jane400, myself, and @calebccff. The design for this was written up in #2937 (closed).

Fixes #2937 (closed) Fixes #2913 (closed)

TODO:

• squash commits
• finish migrating earlier rev using new systemd apkbuild vars to use new macro
• write up design of this for wiki, in #2937 (closed)
• Get branch building again.
• Push patches in this branch to edge/master branch
  • !5500 (merged)
• test