Add draft option support for publish in changeset template
Created by: eseliger
Using the introduced triple of true/false/"draft", users can now specify to open a PR in draft mode on the code host.
I'm opening this up for review, but I need to get https://github.com/sourcegraph/campaignutils/pull/3 merged first in order to merge this PR. Hence, the go.mod
file contains some local hackery that I need to override (no pun intended) once merged.
Another PR in the series of https://github.com/sourcegraph/sourcegraph/issues/7998 towards the first milestone, getting the syntax support ready.