Form block doesn't trigger submit event

[chicharr]

Expected Behaviour

When a form is submitted a submit event is triggered for the form.

Actual Behaviour

Forms are submitted by a listener on the click event of the submit button. The payload is generated and POST'ed as a json via fetch API. This prevents the triggering of the submit event.
This behaviour prevents other features such as RUM or Conversion tracking to work automatically, as they listen to submit events

Reproduce Scenario (including but not limited to)

https://www.hlx.live/developer/forms

Steps to Reproduce

1. In your chrome browser open: https://www.hlx.live/developer/forms
2. Open developer tools -> Console and add a submit listener on the form element. e.g.:document.getElementsByTagName('form')[0].addEventListener('submit', (e) => {console.log('form submitted');})
3. Scroll down to the sample form in the page, enter some data and click submit button.
4. Notice that in the browser Console, there is no message form submitted