compat: introduce apkg compat level

in order to allow config file changes without disruption in the future.

Fixes: #48
4 jobs for compat in 4 minutes and 49 seconds (queued for 8 seconds)
Status Job ID Name Coverage
  Test
passed #536893
flake8

00:03:14

passed #536894
pylint

00:03:36

passed #536896
self

00:03:41

passed #536895
unit

00:04:49