Create a Skip list for yum importer
Yum importer offers a "skip" option to skip certain content types. Theory is that we may use this to skip srpms in the future.
So as a Runcible User I want to be able to skip certain content types.
Fixes #22802 - Add 'skip' option to yum
Yum importer offers a "skip" option to skip certain unit types while
syncing (like rpms, drpms etc )
This commit is to make that available to katello and other projects