Support for publishing a branch

When reintegrating a branch document, the branch document gets 'pushed' over the master version.

However, when publishing a branch document, it depends what happens:

1) If there is not yet a published version below the handle, the branch doc needs to get normal publication (where the live becomes the branch doc). Note that this must EVEN be possible when someone else is editing a different branch! This is similar to the reintegrate workflow except that at the end, the branchInfo is not removed from the document.
2) If there is already a live, only a '

-live version in version history needs to be created

This is because by default, when we publish a branch, it does not replace the published variant if already present

Also note that normal #publish workflow is disabled when the document variant is for a branch, see REPO-2005