[PLT-840] Add option to outgoing webhooks to reply to the posted message as a comment (#7807)

model/outgoing_webhook.go

@@ -46,13 +46,16 @@ type OutgoingWebhookPayload struct {
 }
 
 type OutgoingWebhookResponse struct {
-	Text     *string         `json:"text"`
-	Username string          `json:"username"`
-	IconURL  string          `json:"icon_url"`
-	Props    StringInterface `json:"props"`
-	Type     string          `json:"type"`
+	Text         *string         `json:"text"`
+	Username     string          `json:"username"`
+	IconURL      string          `json:"icon_url"`
+	Props        StringInterface `json:"props"`
+	Type         string          `json:"type"`
+	ResponseType string          `json:"response_type"`
 }
 
+const OUTGOING_HOOK_RESPONSE_TYPE_COMMENT = "comment"
+
 func (o *OutgoingWebhookPayload) ToJSON() string {
 	b, err := json.Marshal(o)
 	if err != nil {