Automatically migrate Solr cores when the major version changes

A given version of Solr only support the current and previous major version of Solr core schema so if you start upgrading XWiki to a version which has Solr 9 it won't be able to read Solr 7 cores.

The current strategy is to recreate the solr search core and to reindex, but that does not work for core which cannot fully be recreated because they contain exclusive data (rating for example). We did not yet have the problem because we started introduce new cores when XWiki was using Solr 8.x, and it currently still use Solr 8.x, but we should fix that ASAP to avoid bad surprises in the future...