UI: Create webhook form test delivery not honoring SSL verification; wrong content-type

[shwstppr]

problem

When creating a Webhook, CloudStack sends a test delivery. Currently it is sending plain text and not honoring SSL verification flag

versions

4.20+

The steps to reproduce the bug

1. Go to create webhook form, enter values for payload url
2. On the server which is listening webhook, observe test payload with plain text data - true and plain/text as Content-Type
3. SSL verification flag is also not correctly honored for the test delivery
   ...

What to do about it?

Form should send a JSON payload as many webhook integrations strictly expect Content-Type as application/json.