Add a 'number of lines of merge conflict' field

[yuvipanda]

This is a new field we could add that lists the total size of various merge conflicts. This allows orgs to sort by this so they can resolve smaller merge conflicts first.

[jasongrout]

Browsing through the graphql api, it doesn't look like we have easy access to a size of a merge conflict, only if there is a merge conflict, so I don't think this will be so easy. We could add some heuristics based on the size of the PR, for example.