Add background migration for removing invalid org user records

What does this MR do and why?

This MR is part of a few MR's that will replace the use of Loose Foreign Keys for organization_users table

MR	Description
!169382 (merged)	Add Foreign Key for user_id (NOT VALID)
!180028 (merged)	Add Foreign Key for organization_id (NOT VALID)
This one	Delete invalid organization_users records
TBD	Finalize the job
TBD	Make the FK's VALID

This MR will delete invalidd organization_users records. "Invalid" means: records that refer to an organization or user that does not exist. We don't expect such records but they could exist.

Implementation

• Process all records in organization_users table. For each batch:
  • Find user_id that do not exist in users table and delete those records
  • Find organization_id that do not exist in organizations table and delete those records

References

Related to #493506 (closed)

DELETE queries performance

Delete records because the associated organization does not exist: 18 ms

Delete records because the associated user does not exist: 7 ms

How to set up and validate locally

Created 50 000 random organization_users records with valid and invalid data.

Before:

 ?column? | count
----------+-------
 invalid  |  1976
 valid    | 48024
(2 rows)

[1] pry(main)> load 'db/post_migrate/20250304144127_queue_remove_invalid_organization_users.rb'
=> true
[2] pry(main)> QueueRemoveInvalidOrganizationUsers.new.up

The invalid records are removed:

 ?column? | count
----------+-------
 invalid  |     0
 valid    | 48024

MR acceptance checklist

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