Update Kubernetes client-go

[csweichel]

This PR updates the Kubernetes client-go version to v1.20.1 thereby fixing #2689 .
The biggest change is the introduction of context.Context in all Kubernetes API calls. I've followed this strategy while choosing a good context:

• if a context is available already (e.g. because of the original request), use that one
• if we cannot sensibly decide on timeouting/cancelation, add a ctx context.Context to the functions parameters (e.g. workspaceExists, getWorkspaceObjects)
• if the operation happens as part of a reoccurring task, use a default timeout (5 seconds)
• if the operation happens as part of CLI or testing, use context.Background()

It also removes the PodIPSource and ServiceIPSource from ws-daemon. Those two are no longer needed as we've settled on deploying registry-facade as daemonSet.

How to test

1. interact with Gitpod, start a workspace, stop it, open ports.
2. Run the integration tests (cd test/tests && go test -v ./...)

[corneliusludmann]

Change looks good. Workspaces are still starting. 👍