Provide examples for using --filter-keys cbbackupmgr restore

Even though this is just regex, maybe we can provide few examples on how to use "filter-keys" and "filter-values" with cbbackupmgr restore.

Possibly this on page https://docs.couchbase.com/server/6.0/backup-restore/cbbackupmgr-restore.html, and older versions where "filter-keys" and "filter-values" applies.