With "webkit-patch upload" you could get a new bug created from the terminal, it'll ask for a bug title and would fill it properly on the ChangeLog files. It looks "git-webkit upload" doesn't have the functionality to create new bugs, it'd be nice to have it.
<rdar://problem/93522077>
Should already be a thing with https://bugs.webkit.org/show_bug.cgi?id=240139, it's tied to branch creation. *** This bug has been marked as a duplicate of bug 240139 ***