🐛 Search OCR on file sets only

This commit will constrain the IIIF search to only search the file sets
of a work.  This way applications that use all_text_tsimv for both the
file sets and work (to support snippets) will not have the work's text
included in the search which would double the results.

Ref:
- notch8/palni_palci_knapsack#199

app/models/iiif_print/iiif_search_decorator.rb

@@ -26,7 +26,7 @@ def solr_params
       return { q: 'nil:nil' } unless q
 
       {
-        q: "#{q} AND (#{iiif_config[:object_relation_field]}:\"#{parent_document.id}\" OR id:\"#{parent_document.id}\")",
+        q: "#{q} AND has_model_ssim:FileSet AND (#{iiif_config[:object_relation_field]}:\"#{parent_document.id}\" OR id:\"#{parent_document.id}\")",
         rows: rows,
         page: page
       }