Filter on Branch enhancement?

[testlabauto]

Hi!

Thank you for making this! Its very helpful.

One addition that I think would be great that I wanted to ask about was the ability to only send slack messages for runs on the main branch. Of course, this could be more complex, but a minimal solution would just be a flag to say only report on main/master.

Just an idea. If you don't have time, I understand. Maybe I could look at posting a PR for it.