Create stale.yml

[fmauch]

Mark stale issues and PRs automatically

[fmauch]

I've added automatic issue closing.

A couple of exceptions should prevent handling issues with special labels.

@stefanscherzinger could you have a look whether you think this list is complete.

PRs are not closed automatically at all, but only tagged as "Stale".

[fmauch]

@stefanscherzinger I checked output of the debug run and this seems to work as expected. Could you please have another look on the parameters?

[stefanscherzinger]

@fmauch Yes, I'll look into it as soon as possible.