Feature: PublishBlobs to take []blobs

[juligasa]

Problem

In the CLI, right now to create a new document, we do
POST /hm/api/document-update — sends genesis as both change and ref
POST /hm/api/document-update — sends the real change + ref

The first POST is a hack because the route admits just {change,ref}. and the genesis must exist before the ref. Since we cannot send all three blobs at the same time, we send first the genesis as both change and ref and then the real change and ref.

Solution

Just like in comments, we should take blobs[] for documents so that we can upload in one go.

[ericvicenti]

This is old code, I think we should migrate entirely to PublishBlobs