Currently the 'solrbackup' resource assumes that users want backups stored "locally" (i.e. stored on a PV or mounted drive using Solr's LocalFileSystemRepository). These local backups can then optionally be "persisted" - which involves compressing them and shipping them to a different PV or S3 bucket.

But no support exists for using other backup destinations that Solr supports natively, such as GCS (as of 8.9).

We should add this support. Users can configure their GCS-backup settings under solrcloud's backupRestoreOptions object, leaving the solrbackup object relatively untouched (except that any "persistence" section on 'solrbackup' would now be ignored, as we can only easily compress files that are stored locally).