Remove bucket cluster configuration option

[deliahu]

Implementation Notes

• the cluster name is currently used as a prefix for all paths in the bucket; that may no longer be necessary, but could remain as is.

Motivation

Users can confuse the cortex internal bucket with their own which they use to save models

Notes

• Double check that the AWS policy for the Cluster and Cluster management is updated accordingly

[RobertLucian]

Closed by #2151.