Add build for checking the existence of conflict markers

We should introduce a build to check for the existence of merge conflict. This would ensure that we don't miss conflicts and can probably fail quicker than a human scanning the diffs.

<<<<<<<
=======
>>>>>>>

/<{7}[\s\S]*?={7}[\s\S]*?>{7}/g will find a complete set of conflict markers, but we might want to just use /<{7}(?=[\s\S]*?)/g so we can return the line number of the opening marker.