Provide a way for the changesets bot to only watch certain PRs

We only use changesets for PRs which are created off the back of Linear tickets - the branches always have the format feature/xx-nnnn

other PRs don't need changesets as they may change things but don't need to be released.

what would be good is if we could configure a regex for branch names, within the PR bot, so that it doesn't request PRs on non feature PRs.