Make RightsMetadata and InheritableRightsMetadata get Solr field names for #to_solr from Hydra config

Make Hydra::Datastream::RightsMetadata#to_solr use Hydra config to get Solr field names.
Make Hydra::Datastream::InheritableRightsMetadata#to_solr use Hydra config to get Solr field names.
Added permissions and inherited permissions field names to stub Hydra config in hydra-access-controls spec_helper.