PreEnqueue implementation

- Add PreEnqueuePlugin to Scheduler Framework
- Implement PreEnqueuePlugin in scheduler queue
- Implementation of SchedulingGates plugin
- Metrics

pkg/scheduler/framework/runtime/framework.go

@@ -75,6 +75,7 @@ type frameworkImpl struct {
 	snapshotSharedLister framework.SharedLister
 	waitingPods          *waitingPodsMap
 	scorePluginWeight    map[string]int
+	preEnqueuePlugins    []framework.PreEnqueuePlugin
 	queueSortPlugins     []framework.QueueSortPlugin
 	preFilterPlugins     []framework.PreFilterPlugin
 	filterPlugins        []framework.FilterPlugin
@@ -125,6 +126,7 @@ func (f *frameworkImpl) getExtensionPoints(plugins *config.Plugins) []extensionP
 		{&plugins.Bind, &f.bindPlugins},
 		{&plugins.PostBind, &f.postBindPlugins},
 		{&plugins.Permit, &f.permitPlugins},
+		{&plugins.PreEnqueue, &f.preEnqueuePlugins},
 		{&plugins.QueueSort, &f.queueSortPlugins},
 	}
 }
@@ -574,6 +576,11 @@ func updatePluginList(pluginList interface{}, pluginSet config.PluginSet, plugin
 	return nil
 }
 
+// EnqueuePlugins returns the registered enqueue plugins.
+func (f *frameworkImpl) PreEnqueuePlugins() []framework.PreEnqueuePlugin {
+	return f.preEnqueuePlugins
+}
+
 // QueueSortFunc returns the function to sort pods in scheduling queue
 func (f *frameworkImpl) QueueSortFunc() framework.LessFunc {
 	if f == nil {