Move clickhouse from backend-fsn over to clickhouse cluster

[hellais]

Currently we have two different clickhouse production deployments:

1. Which is used by the monolith backend for writing the fastpath tables, which is not replicated
2. New replicated one running on the clickhouse cluster

This issue is about moving all the tables from backend-fsn over to the new clickhouse cluster and flipping the fastpath to start writing to the replicated cluster.

The overview of the steps are:

• Create DDL for backend-fsn tables in the cluster with replication (see: https://docs.ooni.org/devops/runbooks/#replicating-mergetree-tables & https://docs.ooni.org/backend/database/)
• Create all necessary accounts to grant permissions to backend-fsn on the cluster
• Make a snapshot of data in backend-fsn and import it into the cluster
• Flip backend-fsn to write to the cluster
• Import all the data from the previous delta to the new delta
• Monitor hosts for incidents
• Discontinue the backend-fsn clickhouse instance