Add app register command

[bgins]

Summary

Problem

There is currently no way to perform the main function of the CLI, to publish an app to the Fission IPFS node with the ability to access it through a Fission subdomain, within the current Rust code base.

Impact

This is part of the core feature of this app and users would not be able to upload their code at all without it.

Solution

Write a command that asks the Fission server to point a subdomain at a location on the IPFS network.

Details

This feature is to be added during the Cli rewrite in Rust.