Force gitlab_main_clusterwide and gitlab_main_cell to become gitlab_main when perfoming DML and Batched background migrations

Background

Scope batched background migrations to gitlab_s... (!86525 - merged)

Problem

Tables will move from/to gitlab_main, gitlab_main_cell, gitlab_main_clusterwide as part of Organization Isolation

Ask

Could we make an update to consider:

restrict_gitlab_migration gitlab_schema: :gitlab_main_clusterwide
restrict_gitlab_migration gitlab_schema: :gitlab_main_cell
restrict_gitlab_migration gitlab_schema: :gitlab_main

queue_batched_background_migration(..., gitlab_schema: :gitlab_main_clustewide)
queue_batched_background_migration(..., gitlab_schema: :gitlab_main_cell)
queue_batched_background_migration(..., gitlab_schema: :gitlab_main)

as all equivalent ? Essentially we force gitlab_main_clustewide and gitlab_main_cell to become gitlab_main when perfoming DML and Batched background migrations.

Proposal

TBC, see &15232 (comment 2197605458)

• Consider formalising this in db/gitlab_schema YAML, instead of hard-coding values.