feat: Introduce kraft cloud subcommand

[jake-ciolek]

Prerequisite checklist

• Read the contribution guidelines regarding submitting new changes to the project;
• Tested your changes against relevant architectures and platforms;
• Ran make fmt on your commit series before opening this PR;
• Updated relevant documentation.

Description of changes

This new subcommand gives users the power to exploit the full potential of Unikraft microVMs by helping them to run and manage instances on the millisecond platform, https://kraft.cloud/.

To get started, sign up for the beta. Once you've received your access token, simply export it via:

export KRAFTCLOUD_TOKEN=...

You can then view available images at individual metros, for example, listing images in Frankfurt:

kraft cloud --metro fra0 img ls

To deploy a new image, package it using kraft pkg and push it to index.unikraft.io:

kraft pkg --name index.unikraft.io/$KRAFTCLOUD_USER/my-app:latest .
kraft pkg push index.unikraft.io/$KRAFTCLOUD_USER/my-app:latest

You can deploy images at any metro via:

kraft cloud --metro fra0 instance create \
	--start \
	--port 80:443 \
	unikraft.io/$KRAFTCLOUD_USER/nginx:latest -- nginx -c /usr/local/nginx/conf/nginx.conf

[nderjung]

🚀