Draft: Prepare achievement_uploads to be fully sharded

What does this MR do and why?

Addresses #398199

• Create trigger for achievement_uploads: set namespace_id from parent achievement when missing
• Add NOT NULL (NOT VALID) constraint on achievement_uploads sharding key: applies to new or updated rows only
• Remove orphan uploads pertaining to deleted achievements and backfill achievement_uploads with sharding key

** Background: achievement_uploads is a partition of uploads

SQL

DELETE FROM "uploads" WHERE ("uploads"."id") IN (SELECT "uploads"."id" FROM "uploads" LEFT JOIN achievements ON achievements.id = uploads.model_id WHERE "uploads"."id" BETWEEN 91 AND 95 AND "uploads"."id" >= 91 AND "uploads"."id" < 92 AND "uploads"."model_type" = 'Achievements::Achievement' AND "achievements"."id" IS NULL)

Query plan: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/44190/commands/135396

UPDATE "uploads" SET created_at = created_at WHERE "uploads"."id" BETWEEN 91 AND 95 AND "uploads"."id" >= 91 AND "uploads"."id" < 92 AND "uploads"."model_type" = 'Achievements::Achievement' AND "uploads"."namespace_id" IS NULL

Query plan: https://postgres.ai/console/gitlab/gitlab-production-main/sessions/44190/commands/135397

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