Rails: Migrate workspaces with config_version=2 to config_version=3 for self-managed

MR: Update config_version & force_full_reconciliati... (!140972 - merged)

Description

In Use default and max workspace resources on work... (!139209 - merged) , all newly created workspaces have config_version=3. On SaaS .com, all existing workspaces with config_version=2 will auto-terminate in 7 days. For self-managed, we need to migrate these non-termianted workspaces to config_version=3 similar to what we have done in Workspace config_version 2 migration (!131402 - merged)

Acceptance Criteria

• A DB migration which will migrate all non-terminated workspace with config_version=2 to config_version=3
• This migration should land on SaaS .com at least 7 days after Use default and max workspace resources on work... (!139209 - merged) is deployed to production.

Impact Assessment

Once this change is deployed, self-managed customers upgrading to this version of gitlab would have all their workspaces restarted to migrate the workspaces. The data within the workspace would be persisted.