Revert "[bug 1388942] Remove support for ES synonyms."
Revert "[bug 1388942] Remove support for ES synonyms."

This reverts commit c7fd9d1d6b867a0feffe826026d1ec3d1ce9fb09.

anushbmx/kitsune,mozilla/kitsune,safwanrahman/kitsune,anushbmx/kitsune,mozilla/kitsune,MikkCZ/kitsune,mozilla/kitsune,safwanrahman/kitsune,MikkCZ/kitsune,MikkCZ/kitsune,safwanrahman/kitsune,anushbmx/kitsune,safwanrahman/kitsune,mozilla/kitsune,MikkCZ/kitsune,anushbmx/kitsune