PLT-2188 Integrations: Support raw new lines in the text payload (#2993)

* Integrations: Support raw new lines in the text payload

* Improve support for raw new lines in text payload

The regexp used to escape control characters now also searches for
additional fields:
text|fallback|pretext|author_name|title|value

api/webhook_test.go

@@ -511,6 +511,7 @@ func TestRegenOutgoingHookToken(t *testing.T) {
 		t.Fatal("should have errored - webhooks turned off")
 	}
 }
+
 func TestIncomingWebhooks(t *testing.T) {
 	th := Setup().InitSystemAdmin()
 	Client := th.SystemAdminClient
@@ -529,11 +530,17 @@ func TestIncomingWebhooks(t *testing.T) {
 	hook = Client.Must(Client.CreateIncomingWebhook(hook)).Data.(*model.IncomingWebhook)
 
 	url := "/hooks/" + hook.Id
+	text := `this is a \"test\"
+	that contains a newline and a tab`
 
 	if _, err := Client.DoPost(url, "{\"text\":\"this is a test\"}", "application/json"); err != nil {
 		t.Fatal(err)
 	}
 
+	if _, err := Client.DoPost(url, "{\"text\":\""+text+"\"}", "application/json"); err != nil {
+		t.Fatal(err)
+	}
+
 	if _, err := Client.DoPost(url, fmt.Sprintf("{\"text\":\"this is a test\", \"channel\":\"%s\"}", channel1.Name), "application/json"); err != nil {
 		t.Fatal(err)
 	}
@@ -552,6 +559,10 @@ func TestIncomingWebhooks(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	if _, err := Client.DoPost(url, "payload={\"text\":\""+text+"\"}", "application/x-www-form-urlencoded"); err != nil {
+		t.Fatal(err)
+	}
+
 	attachmentPayload := `{
         "text": "this is a test",
         "attachments": [