Protect against impossible metadata store configurations

[kyle-sammons]

Summary

We recently ran into a situation where we accidentally had ASTRA_ETCD_ENABLED: false, but also had ASTRA_DATASET_METADATA_STORE_MODE: ETCD_CREATES. This was resulting in NPEs being thrown when the recovery nodes went to rollover a chunk. While the fix in our configuration was easy, it went undetected for longer than it should have. This PR fixes that and prevents the node from booting if an impossible metadata store configuration occurs. We already do similar checks in other places, this was just a gap in our logic

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.