Mark tables as exempt from sharding

What does this MR do and why?

Mark the following tables as exempt from sharding.

• ci_job_artifact_states
• ci_secure_file_states
• dependency_proxy_blob_states
• dependency_proxy_manifest_states
• group_wiki_repositories
• group_wiki_repository_states
• lfs_objects
• lfs_object_states
• merge_request_diff_details
• pages_deployment_states
• pool_repositories
• project_repositories
• project_states
• snippet_repositories
• snippet_repository_states
• upload_states

For these tables, this MR does the following:

1. In db/docs/, change the schema to gitlab_main_cell_local or gitlab_ci_cell_local for these tables.
2. In db/docs/, remove exempt_from_sharding: true since it is implied by the schema.
3. In db/docs/, remove sharding_key: or desired_sharding_key: attributes from these tables.
4. In db/docs/, add sharding_key_issue_url for these tables which don't have a non-nullable organization_id, namespace_id, or project_id with loose foreign key constraint.
   • Exception: Do not attempt to add these columns to lfs_object_states. LFS storage must be rearchitected, or specially handled by Cells and Org Mover, or both.

References

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• Relates to #515383 (closed)
• Relates to #520191

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