ttl: better handling of inbound FK with ON DELETE RESTRICT

After #101376, the TTL job will fail if the TTL table has an inbound FK with the `ON DELETE RESTRICT` option and a row references the TTL table.

Some options to fix this:
1) Add an `ON FOREIGN KEY REFERENCE DO NOTHING` syntax to the `DELETE` statement. See https://www.cockroachlabs.com/docs/v22.2/insert#do-not-update-values-on-conflict
2) Filter these rows out in the TTL job
```
DELETE FROM ttl_table ttl WHERE ttl.fk NOT IN (SELECT other.fk FROM other_table other WHERE other.fk IS NOT NULL)
```

Jira issue: CRDB-26916

Epic CRDB-18322