Separate indexer db to its own postgresql cluster

Move indexer db to its own cluster.

Unfortunately, when separated from the storage db, it has been moved to the replica cluster (T867). As the replication tool backups the cluster fully, that would mean yet another replication of the replica db which is a nogo (due to disk space!).

That will ease its backup (#880).

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Migrated from T944 (view on Phabricator)