Copy stats types from upstream.

This drops another dependency on k8s.io/kubernetes.
This does have the unfortunate side effect that implementers will now
get a compile error until they update their code to use the new type.

Just as a note:

The stats types have moved to k8s.io/kubelet, however the stats types
are only there as of v1.20.
Currently we support older versions than v1.20, and even our go.mod
imports from v1.19.

For now we copy the types in. Later we can remove the type defs and
change them to type aliases to the k8s.io/kubelet types (which prevents
another compile time issue).

Anything relying on type assertions to determine if something implements
this method will, unfortunately, be broken and it will be hard to notice
until runtime. We need to make sure to call this out in the release
notes.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

internal/test/e2e/framework/stats.go

@@ -5,8 +5,8 @@ import (
 	"encoding/json"
 	"strconv"
 
+	stats "github.com/virtual-kubelet/virtual-kubelet/node/api/statsv1alpha1"
 	"k8s.io/apimachinery/pkg/util/net"
-	stats "k8s.io/kubernetes/pkg/kubelet/apis/stats/v1alpha1"
 )
 
 // GetStatsSummary queries the /stats/summary endpoint of the virtual-kubelet and returns the Summary object obtained as a response.