As part of building cells, we have moved quite a few tables to either `main_clusterwide` or `main_cell`. Some of these tables have foreign key relations that are cross-database and should not be allowed to exist. And hence, these FKs must be converted to loose foreign keys. This needs to be done per iteration. So, this issue only acts as a container and anything that falls under a specific iteration needs to be moved to their own epic. For example, all issues that needs to be completed as part of iteration 2 is under a different epic: https://gitlab.com/groups/gitlab-org/-/epics/11179