add v1alpha2 registry based conversion (#1006)

* add v1alpha2 registry based conversion

* test defaults, set our 1st explicit default

* fix typos and dates

* move pluginregistry to its own dir

* remove unused v1alpha2.Namespace type

* move migration code folders, remove switch

* validate internalPolicy a single time

* remove structured logs

* simplify return

* check for nil methods

* properly check before adding default evictor

* add TODO comment

* bump copyright year

pkg/framework/pluginregistry/pluginregistry.go

@@ -0,0 +1,60 @@
+/*
+Copyright 2023 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package pluginregistry
+
+import (
+	"k8s.io/apimachinery/pkg/runtime"
+	"k8s.io/klog/v2"
+	"sigs.k8s.io/descheduler/pkg/framework"
+)
+
+var PluginRegistry Registry
+
+type PluginUtilities struct {
+	PluginBuilder PluginBuilder
+	// Just an example instance of this PluginArg so we can avoid having
+	// to deal with reflect Types
+	PluginArgInstance  runtime.Object
+	PluginArgValidator PluginArgValidator
+	PluginArgDefaulter PluginArgDefaulter
+}
+
+type PluginBuilder = func(args runtime.Object, handle framework.Handle) (framework.Plugin, error)
+
+type (
+	PluginArgValidator = func(args runtime.Object) error
+	PluginArgDefaulter = func(args runtime.Object)
+)
+
+type Registry = map[string]PluginUtilities
+
+func NewRegistry() Registry {
+	return Registry{}
+}
+
+func Register(name string, builderFunc PluginBuilder, exampleArg runtime.Object, pluginArgValidator PluginArgValidator, pluginArgDefaulter PluginArgDefaulter, registry Registry) {
+	if _, ok := registry[name]; ok {
+		klog.V(10).InfoS("Plugin already registered", "plugin", name)
+	} else {
+		registry[name] = PluginUtilities{
+			PluginBuilder:      builderFunc,
+			PluginArgInstance:  exampleArg,
+			PluginArgValidator: pluginArgValidator,
+			PluginArgDefaulter: pluginArgDefaulter,
+		}
+	}
+}