Bug 35138: Add the ability to manage ES facets

Bug 35138: Add the ability to manage ES facets

This new feature allows to manage facets for Elasticsearch from the
administration page.
Prior to this the facet fields were hardcoded in the codebase.

Librarians can then add/remove facet fields and modify their label.

Test plan:
1. Create a new search field and set it a label different than its name.
2. Save
3. Go the bibliographic mapping tab
4. Add 1+ mapping for this search field (Searchable and facetable must be "Yes")
5. Add, reorder, remove new facets
6. Save and reindex your records
7. Search and notice the new facet list

QA: There are several wrong things in this area (ES + facets code,
everything, pm, pl, tt AND on this administration page). I have done my
best to clean the code as much as I could and keep the code cleaner
after than before. But there are still a lot to do.
There are still inconsistencies on this page (like we need to save to
see the changes applied to the other tables), but this is clearly out of
the scope of this bug report.
Another enhancement would be to move the facet list to a different DB
table, that could bring more flexibility:
  * display or not (could be opac/staff/both/none)
  * define the size per field (number of facet to display)
  * order: move search_field.facet_order to this new table.
But, again, it's a lot more work.

More work is done in this area, please see related bug reports.

Sponsored-by: The Research University in the Helmholtz Association (KIT)
Signed-off-by: Clemens Tubach <clemens.tubach@kit.edu>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>