ttljob: add hint to use PK in delete/select query

This will help avoid choosing a plan that scans a secondary index, which
can lead to many KV rows being scanned and also lead to contention.

This updates the query used for both SELECTs and DELETEs so that they
use the primary index.

Release note (bug fix): Fixed a bug that could cause DELETE queries sent
by the row-level TTL job to use a secondary index rather than the
primary index to find the rows to delete. This could lead to some DELETE
operations taking a much longer time than they should. This bug was
present since v22.2.0.

pkg/sql/ttl/ttljob/ttljob_processor.go

@@ -143,7 +143,7 @@ func (t *ttlProcessor) work(ctx context.Context) error {
 			return errors.Wrapf(err, "error fetching table relation name for TTL")
 		}
 
-		relationName = tn.FQString()
+		relationName = tn.FQString() + "@" + lexbase.EscapeSQLIdent(primaryIndexDesc.Name)
 		return nil
 	}); err != nil {
 		return err