[Feature request] "exclude checks" flag

[pznamensky]

Hey guys, awesome tool. Thank you for it!

We're using it in CI for our projects and it works great.
Sometimes we add checks for projects which are optional and it's okay for them to fail and thus they might be skipped.
It looks like right now we can set only a list of required checks via --check ... and it works.

However, from time to time we can add new checks and remove others and we tend to forget to maintain that list of allowed checks.

So, I thought that it might be easier and less error prune to maintain a list of checks which might be excluded.
In this scenario, there is no chance to forget to add a new required check.
Also, from my perspective it's safer to maintain "exclude" list and forget to add some checks to excludes instead of forgetting to add a required check.

Unfortunately, I can't create a PR for that.
But if anyone could do it, I think it would be helpful not only for us.