Add status command for getting current context of the CLI

[bupd]

Summary

Currently, we have no idea which user we logged in as and which registry we are connected to.

Given this we need something like

./harbor-cli status

Cli currently logged in as user_1 to registry demo.goharbor.io

Achieving the below output would be really better

./harbor-cli status

Harbor CLI Status:
==================
Logged in as: user_1
Registry: demo.goharbor.io
API Version: v2.0
Authentication: Token-based
Connected As: user_1 (admin)

Previously Logged in to the following registries:
- demo.goharbor.io 
- another-registry.io

CLI Version: 0.0.3
OS: Linux (x86_64)

[rizul2108]

Can I work on this ? @bupd

[bupd]

There is already a PR that could potentially have a partial fix. but we can take it from there. #275

[rizul2108]

So should i wait for that PR to be merged?