ci: implement lint & Annoyatron

We want to run a linter on CI submission.

We also want to display nice error messages to the user. Thus,
annoyatron is born.

The flow is as follows:
 - a MR is submitted and triggers the 'lint' pipeline
 - annoyatron gets pinged over https that an MR requires attention
 - annoyatron starts running and waits until the MR's pipeline run
   succeeds or fails
 - the lint jobs either succeeds or fails
 - annoyatron notices the pipeline passed, and inspects its results to
   see if the lint pipeline failed or not.
 - annoyatron posts a comment, if necessary