Transformers: Support adding the row index using calculate field transformer (#65148)

public/app/features/transformers/editors/CalculateFieldTransformerEditor.tsx

@@ -37,6 +37,7 @@ interface CalculateFieldTransformerEditorState {
 const calculationModes = [
   { value: CalculateFieldMode.BinaryOperation, label: 'Binary operation' },
   { value: CalculateFieldMode.ReduceRow, label: 'Reduce row' },
+  { value: CalculateFieldMode.Index, label: 'Row index' },
 ];
 
 const okTypes = new Set<FieldType>([FieldType.time, FieldType.number, FieldType.string]);