Put v3 protobuf header in the front of documents

Now that the Node SDK has standardized the protobuf header to use for CMK does, we should put this header on the to the front of documents created via Java as well to make things consistent.

NOTE: As of today, documents encrypted with NodeJS cannot be decrypted with the Java client because the Java client expects the doc header to be empty.

Start by locating Java document creation and the existing v3 protobuf header handling, using the Node SDK behavior described in the issue as the compatibility reference. Done means Java-created documents include the header and documents encrypted with NodeJS can be decrypted by the Java client.

Scritto dal modello di indicizzazione a partire dal testo della issue.