Move @kinvolk/headlamp-plugin to @headlamp-k8s/headlamp-plugin

[joaquimrocha]

We should move the headlamp-plugin program to the @headlamp-k8s org.

[sniok]

We could consider having a create-headlamp-plugin package to take advantage of the npm create command. That way we could create plugin using npm create headlamp-plugin. This is commonly used in another packages for example npm create react-app. Yes, it's just an alias but it'll make creating new plugins a bit more convenient.

https://docs.npmjs.com/cli/v10/commands/npm-init