Alerting: Fix UI bug when setting custom notification policy group by (#54607)

Custom values were not being displayed in the multiselect for notification policy `Group by` even though
they were correctly being saved.

public/app/features/alerting/unified/components/amroutes/AmRootRouteForm.tsx

@@ -87,7 +87,7 @@ export const AmRootRouteForm: FC<AmRootRouteFormProps> = ({
                     setValue('groupBy', [...field.value, opt]);
                   }}
                   onChange={(value) => onChange(mapMultiSelectValueToStrings(value))}
-                  options={[...commonGroupByOptions, groupByOptions]}
+                  options={[...commonGroupByOptions, ...groupByOptions]}
                 />
               )}
               control={control}

public/app/features/alerting/unified/components/amroutes/AmRoutesExpandedForm.tsx

@@ -180,7 +180,7 @@ export const AmRoutesExpandedForm: FC<AmRoutesExpandedFormProps> = ({ onCancel,
                       setValue('groupBy', [...field.value, opt]);
                     }}
                     onChange={(value) => onChange(mapMultiSelectValueToStrings(value))}
-                    options={[...commonGroupByOptions, groupByOptions]}
+                    options={[...commonGroupByOptions, ...groupByOptions]}
                   />
                 )}
                 control={control}