[cassandra] Configure staging cassandra and populate backend

Cassandra service is basically configured in puppet. It will need more tuning.

Problematic: Test Cassandra as main backend in staging. We need in parallel a postgresql backend which needs up-to-date with the cassandra backend.

staging:

• Install data model in cassandra (create keyspace with the proper replication factor and strategy) [1]
• Install redis stack to capture replayer problems
• Trigger journal replayer to fill in cassandra at postgresql's current level
• Install reaper (in charge of triggering repairs regularly)
  • Install keyspace
  • Install cluster seed in reaper ui
  • Install reaper application in staging cluster
• Add storage replayer redis configuration so they can report replaying issues
• Reset topics consumption so they replay from scratch
• (ongoing) replayer fill-in cassandra
• scrubber: Configure for cassandra
• Checks

[1]

CREATE KEYSPACE swh WITH replication = {'class': 'NetworkTopologyStrategy', 'sesi_rocquencourt_staging': '3'}  AND durable_writes = true;