Alerting Contact Points: Test Contact Point feature fails for Slack Integration

[camoore1979]

What happened?

When testing a contact point with the Slack Integration, with the contact point in the saved state (the Webhook URL displays "Configured" rather than showing the value of the webhook), running a test fails with this message:

In the Network tab, we see that the request for POST https://grafana.tools.eoilreports.com/api/alertmanager/grafana/config/api/v1/receivers/test is missing the webhook url in it's payload. Here's the payload from cURL:

--data-raw '{"receivers":[{"name":"test","grafana_managed_receiver_configs":[{"settings":{"title":"{{ template \"slack-title\" . }}","text":"{{ template \"slack-body\" . }}"},"secureSettings":{},"type":"slack","name":"test","disableResolveMessage":true,"uid":"VQmcfZa4k"}]}]}' 

Note, it does work when you edit the Webhook URL input before you save (which hides the value). In the Network tab, we can see that the request in this case is not missing the webhook url in it's payload. Here's the payload from cURL:

--data-raw '{"receivers":[{"name":"test","grafana_managed_receiver_configs":[{"settings":{"title":"{{ template \"slack-title\" . }}","text":"{{ template \"slack-body\" . }}"},"secureSettings":{"url":"https://hooks.slack.com/services/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"},"type":"slack","name":"test","disableResolveMessage":true,"uid":"VQmcfZa4k"}]}]}'```

### What did you expect to happen?

I expected for the Test of the Contact Point with Slack Integration to be successful both in the saved and the unsaved state.

### Did this work before?

Yes. It works fine on other Grafana 9.1.4 instances we are running.

### How do we reproduce it?

The following presupposes that you have configured your Slack instance for receiving messages to a channel via webhook. You will need that webhook to test the following.

1. Navigate to Alerting -> Contact points
2. Select +Add contact point.
3. Select "Slack" from the Integration select.
4. Copy the Slack webhook url into the Webhook URL input.
5. Press "Test", then press "Send test notification." That should work!
6. Press "Save contact point." This will return you to the list of Contact points.
7. Select your Contact point from the list.
8. Press "Test", then press "Send test notification." This should result in the error. See screenshot above.


### Is the bug inside a dashboard panel?

No.

### Environment (with versions)?

Grafana: 10.0.3
OS: macOS 13.4.1
Browser: Chrome Version 115.0.5790.114


### Grafana platform?

Kubernetes

### Datasource(s)?

_No response_

[armandgrillet]

This is fixed in Grafana 10.0.4 (unreleased) and 10.1.0 (will be released on August 22nd): #72235