Refactor scheduler config API

Refactor the kube-scheduler configuration API, command setup, and server
setup according to the guidelines established in #32215 and using the
kube-proxy refactor (#34727) as a model of a well factored component
adhering to said guidelines.

* Config API: clarify meaning and use of algorithm source by replacing
modality derived from bools and string emptiness checks with an explicit
AlgorithmSource type hierarchy.
* Config API: consolidate client connection config with common structs.
* Config API: split and simplify healthz/metrics server configuration.
* Config API: clarify leader election configuration.
* Config API: improve defaulting.
* CLI: deprecate all flags except `--config`.
* CLI: port all flags to new config API.
* CLI: refactor to match kube-proxy Cobra command style.
* Server: refactor away configurator.go to clarify application wiring.
* Server: refactor to more clearly separate wiring/setup from running.

Fixes #52428.

cmd/hyperkube/kube-scheduler.go

@@ -17,24 +17,38 @@ limitations under the License.
 package main
 
 import (
+	"flag"
+
+	"k8s.io/apiserver/pkg/server/healthz"
 	"k8s.io/kubernetes/plugin/cmd/kube-scheduler/app"
-	"k8s.io/kubernetes/plugin/cmd/kube-scheduler/app/options"
 )
 
 // NewScheduler creates a new hyperkube Server object that includes the
 // description and flags.
 func NewScheduler() *Server {
-	s := options.NewSchedulerServer()
+	healthz.DefaultHealthz()
+
+	command := app.NewSchedulerCommand()
 
 	hks := Server{
 		name:            "scheduler",
 		AlternativeName: "kube-scheduler",
 		SimpleUsage:     "scheduler",
-		Long:            "Implements a Kubernetes scheduler.  This will assign pods to kubelets based on capacity and constraints.",
-		Run: func(_ *Server, _ []string, stopCh <-chan struct{}) error {
-			return app.Run(s)
-		},
+		Long:            command.Long,
 	}
-	s.AddFlags(hks.Flags())
+
+	serverFlags := hks.Flags()
+	serverFlags.AddFlagSet(command.Flags())
+
+	// FIXME this is here because hyperkube does its own flag parsing, and we need
+	// the command to know about the go flag set. Remove this once hyperkube is
+	// refactored to use cobra throughout.
+	command.Flags().AddGoFlagSet(flag.CommandLine)
+
+	hks.Run = func(_ *Server, args []string, stopCh <-chan struct{}) error {
+		command.SetArgs(args)
+		return command.Execute()
+	}
+
 	return &hks
 }