Add string metadata fields to AAIB
Add string metadata fields to AAIB

With AAIB, we have a few metadata values which are free text and aren't
filterable. This commit adds them to the AAIB schema using the new facet
attrs that I added in a previous commit.

alphagov/manuals-publisher,alphagov/manuals-publisher,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher-rebuild,alphagov/specialist-publisher-rebuild,ministryofjustice/specialist-publisher,alphagov/specialist-publisher,alphagov/specialist-publisher-rebuild,alphagov/manuals-publisher,ministryofjustice/specialist-publisher,alphagov/specialist-publisher,ministryofjustice/specialist-publisher,ministryofjustice/specialist-publisher,alphagov/specialist-publisher