Add a 'background' parameter for requests that are expected to take more than 10 seconds

Tagging a spammer and marking all of its issues as closed/confidential is a lengthy process.

Instead of returning after ~20 seconds, and let gitlab believe that the webhook did not run properly, we should return early and let the process run in the background.

To have a correlation between the request and the actual output, we add a UUID in all of the incoming requests. This uuid is then shown when the command terminates.

We also add the exit code of the command while we are here.