add :basic_metadata to generated work indexer

when we generate valkyrie works with hyrax basic metadata, so we should also
generate the indexer with that schema loaded in.

lib/generators/hyrax/work_resource/templates/indexer.rb.erb

@@ -3,7 +3,7 @@
 # Generated via
 #  `rails generate hyrax:work_resource <%= class_name %>`
 class <%= class_name %>Indexer < Hyrax::ValkyrieWorkIndexer
-  Hyrax::ValkyrieIndexer.register self, as_indexer_for: <%= class_name %>
+  include Hyrax::Indexer(:basic_metadata)
 
   # Uncomment this block if you want to add custom indexing behavior:
   #  def to_solr