Provide service manager with a list of all possible search facets

[caaster]

Understanding that this could change in the future, for right now it would be very helpful to have a list of all possible search facets for an exhibit. I will include this in internal service manager documentation. Thank you.

[corylown]

@caaster here's the current list of possible facet fields (not including any custom fields)
The first value is the Solr field name followed by the default display label if one is configured.

'author_no_collector_ssim', label: 'Author (no Collectors)'
'author_other_facet', label: 'Organization (as author)'
'author_person_facet', label: 'Author' # includes Collectors
'box_ssi', label: 'Box'
'collector_ssim', label: 'Collector'
'era_facet', label: 'Era'
'folder_ssi', label: 'Folder'
'format_main_ssim', label: 'Resource type'
'genre_ssim', label: 'Genre'
'geographic_facet', label: 'Region'
'language', label: 'Language'
'place_created_ssim', label: 'Place created'
'pub_year_no_approx_isi', label: 'Date (no approx)'
'pub_year_tisim', label: 'Date Range'
'pub_year_w_approx_isi', label: 'Date'
'publisher_ssim', label: 'Publisher'
'repository_ssim', label: 'Repository'
'series_ssi', label: 'Series'
'topic_facet', label: 'Topic'

The Donor tags, Folder Name and Document subtype facets below were added as a specific need of the Feigenbaum exhibit.

'collection_with_title', label: 'Collection'
'doc_subtype_ssi', label: 'Document Subtype'
'donor_tags_ssim', label: 'Donor tags'
'folder_name_ssi', label: 'Folder Name'
'related_document_id_ssim'