receiving webhook events should be possible for development purpose

[bavarianbidi]

What is the feature you would like to have?

As a developer of the garm-operator it would be nice to have something implemented to receive webhooks from github.

Anything else you would like to add?

garm uses ngrok for integration tests - this should work for local development purpose as well

xref: https://github.com/cloudbase/garm/blob/f64ffa8d924922231b3b335b02d9a1fa0cc46e5b/.github/workflows/integration-tests.yml#L27-L33