Organization migration: Reduce downtime
## Executive Summary
Integrate external efforts in order to reduce downtime of an organization migration.
#### Engineering Assessment
1. Speed up the script to dump table data for an organization
1. Depends on: https://gitlab.com/groups/gitlab-org/-/epics/11670+
1. Depends on: All large tables have indexed their sharding key
1. Make the organization migration script/playbook use logical replication to replicate PostgreSQL data for an organization
1. Depends on: Siphon supports row-filtered replication of all tables to another PostgreSQL database
#### Dependencies
- Team dependencies:
- ~"group::organizations": https://gitlab.com/groups/gitlab-org/-/epics/11670+
- ~"group::organizations": All large tables have indexed their sharding key
- ?: Siphon supports row-filtered replication of all tables to another PostgreSQL database
epic