fixes #6330 - add with_features(Pulp) to filter content capsules

[isratrade]

No description provided.

[jlsherrill]

Note, this requires a couple things before merge:

• Now that the smart proxy plugin support is there, we need a Pulp feature plugin (this may happen here Implements #4630: SmartProxy can query the status of Pulp server now. theforeman/smart-proxy#153)
• We need a 'Pulp Parent' feature (or something similar, "Master Pulp", "Master Content Source" etc..) for the katello server running the 'default smart proxy' with the main pulp server
• This PR should also check for that feature as well
• puppet-capsule change to enable the 'Pulp' feature (DO NOT MERGE addresses #6226 - enable the pulp configuration value in the proxy theforeman/puppet-foreman_proxy_content#9)
• puppet-capsule change to enable the 'Pulp Parent' feature

[jlsherrill]

Closing in favor of #4528

Thanks @isratrade !