Update request status based on GitHub email updates

[karelstriegel]

An additional way of updating request statusses is by signing up for the status updates of issues that are linked to a request, by scanning the update emails of those requests we have an extra way of updating the status of the request, without having the call the github api.

This should of course be investigated.

Thx @nico-ptrs for the suggestion

[davy-vr]

check https://cloud.spring.io/spring-cloud-stream/