LP#1673857: add search filter for copy_tags

LP#1673857: add search filter for copy_tags

Copy tags can be used as a search filter in the catalog. Two
variations are supported:

* copy_tag(type_code, search_terms)

  Search for records that have copies that are linked to tags
  whose value matches the search terms and whose type's
  config.copy_tag_type.code matches the specified
  type_code. E.g., "copy_tag(bookplate, donated by jane smith)"

* copy_tag(*, search_terms)

  Search for records that have copies that are linked to tags
  whose value matches the search terms, regardless of type.

The copy_tag() search filter takes the OPAC-visiblity (as determined
by asset.copy_tag.pub) of the tag into account.

Mike Rylander also contributed to this patch.

Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>
Signed-off-by: Josh Stompro <stomproj@larl.org>
Signed-off-by: Galen Charlton <gmc@equinoxinitiative.org>