Deprecate feature to configure indexing for a property when defined in model

[hackartisan]

Descriptive summary

Instead people will need to write indexers that explicitly handle each property.

Rationale

Valkyrie models do not allow this type of configuration. Indexing this way is a blocker for removing active fedora dependency.

Related work

#3800

[no-reply]

This is to deprecate the following index configuration style:

property :title, predicate: RDF::DC.title do |index|
  index.as :discoverable, :stored_searchable
end

in favor of:

class MyWork < ActiveFedora::Base
  self.indexer = MyWorkIndexer
end