Revert "stack/monitor: cleanup deprecated (and confusing) config"

This reverts commit f34aeeab.

this had the side effect of installing `promise-check-free-disk-space` which
is still used - at least by caddy tests.
2 jobs for fix/monitoring-promise-username-password in 0 seconds
Status Job ID Name Coverage
  External
canceled SlapOS.SoftwareReleases.IntegrationTest-Jerome-Python3

02:28:49

canceled SlapOS.SoftwareReleases.IntegrationTest-Jerome-WIP

02:29:53