Use lazy rest mapper

provider-kubernetes initialized a new kubernetes client for each
reconcile. The REST mapper in controller-runtime used to fetch
information about every CRD in the cluster.

controller-runtime introduced a lazy restmapper which means we don't
have to introduce any complex caching to get a significant performance
boost in provider-kubernetes:

kubernetes-sigs/controller-runtime#2116

This seems to become the default in the next release:

kubernetes-sigs/controller-runtime#2296

But this is so significant that we want to update now:

* CPU reduced from constant throttling at 0.4 cores to 0.04 cores

* CloudWatch / EKS audit log costs reduced significantly (55% for our
  cluster, with a lot of provider-kubernetes resources)

Signed-off-by: Carl Henrik Lunde <chlunde@ifi.uio.no>

internal/clients/client.go

@@ -19,6 +19,7 @@ import (
 	"k8s.io/client-go/tools/clientcmd"
 	"k8s.io/client-go/tools/clientcmd/api"
 	"sigs.k8s.io/controller-runtime/pkg/client"
+	"sigs.k8s.io/controller-runtime/pkg/client/apiutil"
 )
 
 // NewRESTConfig returns a rest config given a secret with connection information.
@@ -33,7 +34,14 @@ func NewRESTConfig(kubeconfig []byte) (*rest.Config, error) {
 // NewKubeClient returns a kubernetes client given a secret with connection
 // information.
 func NewKubeClient(config *rest.Config) (client.Client, error) {
-	kc, err := client.New(config, client.Options{})
+	// in 0.15 this will be default
+	mapper, err := apiutil.NewDynamicRESTMapper(config, apiutil.WithExperimentalLazyMapper)
+	if err != nil {
+		return nil, errors.Wrap(err, "cannot create dynamic REST mapper for Kubernetes client")
+	}
+	kc, err := client.New(config, client.Options{
+		Mapper: mapper,
+	})
 	if err != nil {
 		return nil, errors.Wrap(err, "cannot create Kubernetes client")
 	}