SOLR filter tags (facet counts remain static with `q`)

[nickdos]

See https://stackoverflow.com/a/40760190/249327.

https://solr.apache.org/guide/8_0/faceting.html#tagging-and-excluding-filters

Using this approach the filter drop down lists will not change when one is selected.

Also described at https://blog.griddynamics.com/multi-select-faceting-for-nested-documents-in-solr/

[nickdos]

Done and deployed