Create content (pulp) feature and 'default content' feature in pluggable smart proxy
For the issues discussed here https://github.com/Katello/katello/pull/4282
we need a two new features in the smart proxy:
Content (aka Pulp Node)
Default Content (aka master pulp server running on katello server)
The reason we need both is that the smart proxy on the master pulp server should not be able to have lifecycle environments added or removed from them. It would also help identifying the 'default capsule'