Database configs store a "bucket" field - which in most cases points to the "owning" bucket of the config.

This assumption falls apart when a bucket's contents (including dbconfig) are moved to another bucket (via backup/restore or XDCR)

We should enforce the "bucket" field in the dbconfig matches on both insert (which we already do), and on load to prevent backed up/restored buckets from being used by SG unintentionally.

Need to ensure that databases and config config overwrite is allowed for already existing and mismatched configs (e.g. a backup/restored bucket can be used after an explicit update to fix the bucket field)