Add external database role and pipeline

[ehelms]

This should help with testing external database use cases. I used it to test the EVR removal (theforeman/foreman-installer#984).

[ianballou]

I hit an error when trying it out:

TASK [foreman_installer : Run installer] *********************************************************************************************************************
fatal: [pi-katello-nightly-centos9-stream-server]: FAILED! => changed=true 
  cmd: |-
    foreman-installer -v --no-colors   --scenario katello  --foreman-db-manage false --foreman-db-host pi-katello-nightly-centos9-stream-database --foreman-db-database foreman --foreman-db-password foreman --katello-candlepin-manage-db false --katello-candlepin-db-host pi-katello-nightly-centos9-stream-database --katello-candlepin-db-name candlepin --katello-candlepin-db-password candlepin --foreman-proxy-content-pulpcore-manage-postgresql false --foreman-proxy-content-pulpcore-postgresql-host pi-katello-nightly-centos9-stream-database --foreman-proxy-content-pulpcore-postgresql-db-name pulp --foreman-proxy-content-pulpcore-postgresql-password pulp
  delta: '0:00:00.303296'
  end: '2024-11-04 15:00:30.247603'
  msg: non-zero return code
  rc: 26
  start: '2024-11-04 15:00:29.944307'
  stderr: 'ERROR: Scenario (/etc/foreman-installer/scenarios.d/katello.yaml) was not found, can not continue'
  stderr_lines: <omitted>
  stdout: ''
  stdout_lines: <omitted>

Looks like the Katello installer module wasn't installed for some reason.