[FEATURE] Added synonym management to SolrService

Since Solr 4.8 there is a REST API to get and
set synonyms. Delete method is missing.

Related: #58173
Change-Id: I37eebf9ac3575693237994a4ec6be53ed862ec56
Reviewed-on: https://review.typo3.org/30194
Reviewed-by: Ingo Renner
Tested-by: Ingo Renner