Add DeleteMigrateSharedVulnerabilityScanners migration

What does this MR do and why?

!89127 (merged) introduced the MigrateSharedVulnerabilityScanners background migration which suffers from a long runtime due to a bug.

Because the migration has accumulated ~12283 job rows, deleting the migration row from batched_background_migrations will also delete all 12k rows from batched_background_migration_jobs due to ON CASCADE DELETE.

This MR adds a Post Deployment Migration which (1) deletes the job rows from batched_background_migration_jobs in batches, and (2) deletes the migration row from batched_background_migrations.

Database queries

(cold caches)

SELECT
	"batched_background_migration_jobs"."id"
FROM
	"batched_background_migration_jobs"
	INNER JOIN "batched_background_migrations" "batched_background_migration" ON "batched_background_migration"."id" = "batched_background_migration_jobs"."batched_background_migration_id"
WHERE
	"batched_background_migration"."job_class_name" = 'MigrateSharedVulnerabilityScanners'
ORDER BY
	"batched_background_migration_jobs"."id" ASC
LIMIT 500;

postgres.ai

---

DELETE FROM "batched_background_migration_jobs"
WHERE "batched_background_migration_jobs"."id" IN(
		SELECT
			"batched_background_migration_jobs"."id" FROM "batched_background_migration_jobs"
			INNER JOIN "batched_background_migrations" "batched_background_migration" ON "batched_background_migration"."id" = "batched_background_migration_jobs"."batched_background_migration_id"
		WHERE
			"batched_background_migration"."job_class_name" = 'MigrateSharedVulnerabilityScanners'
			AND "batched_background_migration_jobs"."id" >= 1000
			AND "batched_background_migration_jobs"."id" < 1500);

postgres.ai

---

DELETE FROM "batched_background_migrations"
WHERE "batched_background_migrations"."job_class_name" = 'MigrateSharedVulnerabilityScanners'
	AND "batched_background_migrations"."table_name" = 'vulnerability_occurrences'
	AND "batched_background_migrations"."column_name" = 'id'
	AND(job_arguments = '[]'::jsonb)
	AND "batched_background_migrations"."gitlab_schema" = 'gitlab_main';

• with associated rows in batched_background_migration_jobs: postgres.ai (5.405 s)
• without associated rows: postgres.ai (24.990 ms)

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.