Move cloud metadata packages and kubernetes resources marshaling to internal

Decouples cloud provider metadata packages from kubernetes related code

Signed-off-by: Malte Poll <mp@edgeless.systems>

internal/cloud/gcp/cloudnodemanager_test.go

@@ -0,0 +1,17 @@
+package gcp
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestTrivialCNMFunctions(t *testing.T) {
+	assert := assert.New(t)
+	cloud := CloudNodeManager{}
+
+	assert.Empty(cloud.Image(""))
+	assert.Empty(cloud.Path())
+	assert.Empty(cloud.ExtraArgs())
+	assert.False(cloud.Supported())
+}