Support using `pushRemote` and `merge` to detect the PR of a branch

[rynoV]

My branches are set up like this (a triangle workflow, but with just one remote):

[branch "feature1"]
	pushRemote = origin
	remote = origin
	merge = refs/heads/master
[branch "feature2-using-feature1"]
	pushRemote = origin
	remote = origin
	merge = refs/heads/feature1

Currently it seems like this plugin is matching the "merge" setting of the branches against the "from" setting of the PR to decide which branch should be checked-out for a PR. However this results in feature2-using-feature1 being associated with feature1's PR.

I couldn't find a setting to make this work. I'm working around it by going into .git/config and manually updating the vscode-merge-base and github-pr-owner-number settings for each branch, but it would be great if there's some way to configure this plugin so that PRs can be associated with branches based on the pushRemote setting and matching names of the local branches with those on the pushRemote (https://git-scm.com/docs/git-config#Documentation/git-config.txt-branchnamepushRemote)