Change predicate used by keyword

[ghost]

Fixes #1505

• Change the predicate in BasicMetadata
• Add a migration service for changing predicates and rake task for the current change

The migration service updates the graph, moving data from the previous predicate to the new one, eg.

Hyrax::Works::MigrationService.migrate_predicate(
  ::RDF::Vocab::DC11.relation,
  ::RDF::Vocab::SCHEMA.keywords
)

For keywords, this changewill require running the following rake task and needs to be added to the release notes for this version:

rake hyrax:migrate:migrate_keyword_predicate

Note Rubocop complains about the use of @work in the test, hence the disable / enable statements. Using let the test fails - the predicates don't get updates. I am not sure why.