Deprecate `stahnma-epel` and use VoxPupuli's `puppet-epel`
By accepting and applying this merge request we will be able to:
- no longer use a deprecated module to deal with EPEL;
- track a currently supported module maintained by Vox Pupuli.
The version of puppet-freeipa
was intentionally not updated, so upstream's developers decide on bumping it once the patches are applied.