Add synonym support

[kevinquillen]

The current Search API Synonyms module only deals with importing and exporting synonyms in a generic way. There are no specific ties to any particular backend. I don't think this would suit how Typesense structures and relates synonyms and I would prefer them to be saved to Typesense when they are created/edited/removed along with a 'sync all' button that performs a mass upsert.