API V2: Transaction endpoint

[cdamus]

The design of the Node.js façade for the Model Server required an API endpoint for self-composing sequential units of model edit. This was implemented in the Java server as an api/v2/transaction. Because it was originally intended that only this new server layer use this new endpoint, and not yet supported for use by client applications, the transaction endpoint was specifically excluded from the Java client API, including in PR #196 which otherwise completes the Client API v2.

So, this feature request asks for a definitive position on support for this transaction endpoint to be resolved by one of

• adding it to the Java client API ModelServerClientApiV2, thus officially supporting its use by client applications
  • this might then warrant a contribution also to the Javascript Client API to port the transaction support from modelserver-node's internal custom API client class to the public API
• documenting that it is for internal use server-side only by model server-node
• documenting that it is available for provisional, unsupported use by client applications via HTTP without convenience API support
• some other resolution not mentioned here