dev.knotless.getMergeStatus

Whether an open pull can merge now, decided as `knotless pull merge` decides it, without merging: whether its head merges with its target branch as it is now, and, in a repository that names runners, whether each workflow that runs on it passed there. And what the account asking may do to it: merge it, queue it, retarget it or run its checks again. Requires the session cookie the pages' login sets, or a service token from the caller's PDS, audience the appview's DID, for this method.