MM-10352: Add locking incoming webhooks to a single channel. (#8835)

app/webhook.go

@@ -633,6 +633,10 @@ func (a *App) HandleIncomingWebhook(hookId string, req *model.IncomingWebhookReq
 		}
 	}
 
+	if hook.ChannelLocked && hook.ChannelId != channel.Id {
+		return model.NewAppError("HandleIncomingWebhook", "web.incoming_webhook.channel_locked.app_error", nil, "", http.StatusForbidden)
+	}
+
 	if a.License() != nil && *a.Config().TeamSettings.ExperimentalTownSquareIsReadOnly &&
 		channel.Name == model.DEFAULT_CHANNEL {
 		return model.NewAppError("HandleIncomingWebhook", "api.post.create_post.town_square_read_only", nil, "", http.StatusForbidden)