ref(crons): Drop the check-in monitor_id column

[wedamija]

Part of a series reducing crons database work per check-in, as check-in volume grows.

Drops sentry_monitorcheckin.monitor_id. Its indexes are dropped in #127646. DROP COLUMN only changes the catalog, so it is quick.

Do not merge until #127646 has deployed. Dropping the column while older code still has the field on the model would break it.

Merge order:

1. sentry#127609: Filter check-in list and stats by monitor environment ids
2. sentry#127644: Stop using monitor_id and make it nullable with no FK constraint
3. sentry#127646: Remove the field from the model, drop its indexes concurrently, MOVE_TO_PENDING (after ref(crons): Stop using monitor_id on check-ins #127644 deploys)
4. sentry#127648: Drop the column, DELETE (after 3 deploys and its migration has run) ← this PR

[linear-code]

ID-3

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/monitors/migrations/0020_make_checkin_monitor_nullable.py src/sentry/monitors/migrations/0021_remove_checkin_monitor.py src/sentry/monitors/migrations/0022_drop_checkin_monitor.py

for 0020_make_checkin_monitor_nullable in monitors

--
-- Alter field monitor on monitorcheckin
--
SET CONSTRAINTS "sentry_monitorcheckin_monitor_id_c15ff0f0_fk_sentry_monitor_id" IMMEDIATE; ALTER TABLE "sentry_monitorcheckin" DROP CONSTRAINT "sentry_monitorcheckin_monitor_id_c15ff0f0_fk_sentry_monitor_id";
ALTER TABLE "sentry_monitorcheckin" ALTER COLUMN "monitor_id" DROP NOT NULL;

for 0021_remove_checkin_monitor in monitors

--
-- Remove index sentry_moni_monitor_0a49ce_idx from monitorcheckin
--
DROP INDEX CONCURRENTLY IF EXISTS "sentry_moni_monitor_0a49ce_idx";
--
-- Remove index sentry_moni_monitor_7ed5ce_idx from monitorcheckin
--
DROP INDEX CONCURRENTLY IF EXISTS "sentry_moni_monitor_7ed5ce_idx";
--
-- Moved monitorcheckin.monitor field to pending deletion state
--
-- (no-op)

for 0022_drop_checkin_monitor in monitors

--
-- Remove field monitor from monitorcheckin
--
SET CONSTRAINTS "sentry_monitorcheckin_monitor_id_c15ff0f0_fk_sentry_monitor_id" IMMEDIATE; ALTER TABLE "sentry_monitorcheckin" DROP CONSTRAINT "sentry_monitorcheckin_monitor_id_c15ff0f0_fk_sentry_monitor_id";
ALTER TABLE "sentry_monitorcheckin" DROP COLUMN "monitor_id" CASCADE;

[sentry]

Sentry Snapshot Testing

Name	Added	Removed	Changed	Renamed	Unchanged	Skipped	Status
sentry-frontend sentry-frontend	0	0	0	0	630	0	✅ Unchanged

⚙️ sentry-frontend Snapshot Settings

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/monitors/migrations/0021_make_checkin_monitor_nullable.py src/sentry/monitors/migrations/0022_remove_checkin_monitor.py src/sentry/monitors/migrations/0023_drop_checkin_monitor.py

for 0021_make_checkin_monitor_nullable in monitors

--
-- Alter field monitor on monitorcheckin
--
SET CONSTRAINTS "sentry_monitorcheckin_monitor_id_c15ff0f0_fk_sentry_monitor_id" IMMEDIATE; ALTER TABLE "sentry_monitorcheckin" DROP CONSTRAINT "sentry_monitorcheckin_monitor_id_c15ff0f0_fk_sentry_monitor_id";
ALTER TABLE "sentry_monitorcheckin" ALTER COLUMN "monitor_id" DROP NOT NULL;

for 0022_remove_checkin_monitor in monitors

--
-- Remove index sentry_moni_monitor_0a49ce_idx from monitorcheckin
--
DROP INDEX CONCURRENTLY IF EXISTS "sentry_moni_monitor_0a49ce_idx";
--
-- Remove index sentry_moni_monitor_7ed5ce_idx from monitorcheckin
--
DROP INDEX CONCURRENTLY IF EXISTS "sentry_moni_monitor_7ed5ce_idx";
--
-- Moved monitorcheckin.monitor field to pending deletion state
--
-- (no-op)

for 0023_drop_checkin_monitor in monitors

--
-- Remove field monitor from monitorcheckin
--
SET CONSTRAINTS "sentry_monitorcheckin_monitor_id_c15ff0f0_fk_sentry_monitor_id" IMMEDIATE; ALTER TABLE "sentry_monitorcheckin" DROP CONSTRAINT "sentry_monitorcheckin_monitor_id_c15ff0f0_fk_sentry_monitor_id";
ALTER TABLE "sentry_monitorcheckin" DROP COLUMN "monitor_id" CASCADE;

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/monitors/migrations/0022_remove_checkin_monitor.py src/sentry/monitors/migrations/0023_drop_checkin_monitor.py

for 0022_remove_checkin_monitor in monitors

--
-- Remove index sentry_moni_monitor_0a49ce_idx from monitorcheckin
--
DROP INDEX CONCURRENTLY IF EXISTS "sentry_moni_monitor_0a49ce_idx";
--
-- Remove index sentry_moni_monitor_7ed5ce_idx from monitorcheckin
--
DROP INDEX CONCURRENTLY IF EXISTS "sentry_moni_monitor_7ed5ce_idx";
--
-- Moved monitorcheckin.monitor field to pending deletion state
--
-- (no-op)

for 0023_drop_checkin_monitor in monitors

--
-- Remove field monitor from monitorcheckin
--
ALTER TABLE "sentry_monitorcheckin" DROP COLUMN "monitor_id" CASCADE;

[github-actions]

This PR has a migration; here is the generated SQL for src/sentry/monitors/migrations/0023_drop_checkin_monitor.py

for 0023_drop_checkin_monitor in monitors

--
-- Remove field monitor from monitorcheckin
--
ALTER TABLE "sentry_monitorcheckin" DROP COLUMN "monitor_id" CASCADE;