[MM-15220] Add generic error field to SubmitDialogResponse (#12081)

This will allow integrations to return an generic error message that is
not tied to a specific dialog field.

app/integration_action_test.go

@@ -430,6 +430,7 @@ func TestSubmitInteractiveDialog(t *testing.T) {
 		assert.Equal(t, "value1", val)
 
 		resp := model.SubmitDialogResponse{
+			Error: "some generic error",
 			Errors: map[string]string{"name1": "some error"},
 		}
 
@@ -444,6 +445,7 @@ func TestSubmitInteractiveDialog(t *testing.T) {
 	resp, err := th.App.SubmitInteractiveDialog(submit)
 	assert.Nil(t, err)
 	require.NotNil(t, resp)
+	assert.Equal(t, "some generic error", resp.Error)
 	assert.Equal(t, "some error", resp.Errors["name1"])
 
 	submit.URL = ""

model/integration_action.go

@@ -222,6 +222,7 @@ type SubmitDialogRequest struct {
 }
 
 type SubmitDialogResponse struct {
+	Error  string            `json:"error,omitempty"`
 	Errors map[string]string `json:"errors,omitempty"`
 }
 

model/integration_action_test.go

@@ -141,6 +141,7 @@ func TestSubmitDialogRequestToJson(t *testing.T) {
 func TestSubmitDialogResponseToJson(t *testing.T) {
 	t.Run("all fine", func(t *testing.T) {
 		request := SubmitDialogResponse{
+			Error: "some generic error",
 			Errors: map[string]string{
 				"text":  "some text",
 				"float": "1.2",