BE: Add data store to support namespace-cluster agent mapping for RD

MR: !145101 (merged)

Description

Add the datastore as described in the technical design for the new group-agent mapping feature

Acceptance Criteria

• Add the data store as mentioned in the design doc

Technical Requirements

• Same as the acceptance criteria

Design Requirements

NA

Impact Assessment

• Since the datastore is not expected to be used, there should be no impact on the existing features