feat: build CLI client which can manage contacts, send messages, receive messages

[Meghajit]

When complete, Kau will expose websocket APIs which can be used to deliver and receive messages for a registered user.

As part of this story, the scope is to build a CLI client which can do the following: ( scope is limited as of now, but the client can be enhanced further as more features get added onto Kau)

1. Register/Onboard a user onto Kau
2. Securely login a user into Kau
3. Allow sending a message to another online registered user
4. Allow receiving messages when online from another registered user
5. Show notification indicator when a user has transitioned from OFFLINE -> ONLINE and other users have sent him messages