Configure and clear a ClickHouse Cloud service's scheduled upgrade (maintenance) window via GET/PUT/DELETE upgradeWindow

Documented steps

1. Read the current window: GET /v1/organizations/{organizationId}/services/{serviceId}/upgradeWindow. curl -u "$KEY_ID:$KEY_SECRET" https://api.clickhouse.cloud/v1/organizations/$ORG_ID/services/$SERVICE_ID/upgradeWindow - a 404 means no window has been configured and the service uses default scheduling.
2. Set or fully replace the window with PUT on the same path. The body requires exactly two fields: weekday (integer 0-6, where 0 = Sunday) and startHourUtc (integer, one of 0, 6, 12, 18).
3. curl -u "$KEY_ID:$KEY_SECRET" -X PUT https://api.clickhouse.cloud/v1/organizations/$ORG_ID/services/$SERVICE_ID/upgradeWindow -H 'Content-Type: application/json' -d '{"weekday":2,"startHourUtc":6}' schedules routine upgrades for Tuesdays 06:00-12:00 UTC.
4. The window currently lasts 6 hours from startHourUtc, which is why only 0/6/12/18 are accepted - the four values tile a 24-hour day.
5. Convert your local maintenance preference to UTC yourself, and re-check it after daylight-saving transitions since the API stores UTC only.
6. Restore default scheduling with DELETE on the same path: curl -u "$KEY_ID:$KEY_SECRET" -X DELETE https://api.clickhouse.cloud/v1/organizations/$ORG_ID/services/$SERVICE_ID/upgradeWindow
7. Separately from timing, control which release cadence is eligible during the window with PATCH /v1/organizations/{organizationId}/services/{serviceId} and {"releaseChannel":"slow"|"default"|"fast"} - 'fast' takes new releases earliest, 'slow' defers them.
8. Verify by re-reading the window with GET and confirming the returned weekday/startHourUtc match what you set.
9. Docs: https://clickhouse.com/docs/manage/updates (scheduled upgrades and release channels) and https://clickhouse.com/docs/cloud/manage/api/api-overview