docs(clickhouse): deleting a Backup on the system bucket now deletes its archive #808

After cozystack/cozystack#5224, deleting a ClickHouse Backup taken on backup.useSystemBucket: true deletes its archive through the clickhouse-backup sidecar, and the documented sidecar delete route is POST /backup/delete/remote/<name>.

Pages to update:

• content/en/docs/next/applications/backup-and-recovery.md says the ClickHouse archive is governed by the sidecar's retention and stays after the Backup is deleted.
• content/en/docs/next/operations/services/backup-classes.md describes archive cleanup for MongoDB and Rabbitmq but not ClickHouse; the ArtifactNotDeleted and ArtifactCleanupFailed Events and the backups.cozystack.io/skip-artifact-cleanup annotation apply to it too.
• content/en/docs/v1.4/operations/services/managed-app-backup-configuration.md documents DELETE /backup/<name>/remote, which clickhouse-backup 2.7 does not serve; the route is POST /backup/delete/remote/<name>.