Provide better cluster access information to customers in portal

[marians]

On the cluster details page, currently we only display the Kubernetes API endpoint URL.

Ideally though we want to help customers access the cluster using kubectl (first) and other tools (eventually).

For Giant Swarm staff we currently show instructions on how to set up a kubectl context for the cluster via teleport.

[marians]

IMO the least we should do is provide the correct kubectl gs login command to use