slack notification - allow filtering by branch

[emma-syb]

I might miss something but it looks like the slack notification can not be filtered by branch, making it send alerts for in development branches. I'd like to only receive alerts for increases in the main branch.

[vio]

@emma-syb Thank you for creating the issue! Rule context (branch name, user, etc.) is something we are already planning to add to GitHub reviews and Slack notifications in the near future. Will keep you posted here once we start testing it.

If you have any other feedback or feature requests, feel free to share them here. 🙇