First draft of moving API server TLS cert generation to controllers

- Refactors the existing cert generation code into controllers
  which read and write a Secret containing the certs
- Does not add any new functionality yet, e.g. no new handling
  for cert expiration, and no leader election to allow for
  multiple servers running simultaneously
- This commit also doesn't add new tests for the cert generation
  code, but it should be more unit testable now as controllers

internal/controller/utils.go

@@ -0,0 +1,31 @@
+/*
+Copyright 2020 VMware, Inc.
+SPDX-License-Identifier: Apache-2.0
+*/
+
+package controller
+
+import (
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+
+	"github.com/suzerain-io/controller-go"
+)
+
+func NameAndNamespaceExactMatchFilterFactory(name, namespace string) controller.FilterFuncs {
+	objMatchesFunc := func(obj metav1.Object) bool {
+		return obj.GetName() == name && obj.GetNamespace() == namespace
+	}
+	return controller.FilterFuncs{
+		AddFunc: objMatchesFunc,
+		UpdateFunc: func(oldObj, newObj metav1.Object) bool {
+			return objMatchesFunc(oldObj) || objMatchesFunc(newObj)
+		},
+		DeleteFunc: objMatchesFunc,
+	}
+}
+
+// Same signature as controller.WithInformer().
+type WithInformerOptionFunc func(
+	getter controller.InformerGetter,
+	filter controller.Filter,
+	opt controller.InformerOption) controller.Option