[Feature Request] Support alert routing

Hello again! Back with another feature request.

Something that'd be very handy for us is to be able to set "global" filters on alerts, which would apply to every alert. For example, we want to be able to filter to something like env: "production" on all of our alerts so we don't get spammed with alerts about staging.

I can't see a way to do this right now without setting the filter on every alert separately, but maybe I'm missing it. If I'm not missing something and this isn't possible, I'd be happy to contribute this too!