Add comment for max_values_by_sequence_table map in proto

Signed-off-by: Noble Mittal <[email protected]>

Author: beingnoble03

go/vt/proto/tabletmanagerdata/tabletmanagerdata.pb.go

@@ -989,5 +989,6 @@ message GetMaxValueForSequencesRequest {
 }
 
 message GetMaxValueForSequencesResponse {
+  // Max used sequence value mapped with the backing sequence table.
   map<string, int64> max_values_by_sequence_table = 1;
 }