De-share the Handler struct in core API (#105979)

* De-share the Handler struct in core API

An upcoming PR adds a handler that only applies on one of these paths.
Having fields that don't work seems bad.

This never should have been shared.  Lifecycle hooks are like a "write"
while probes are more like a "read". HTTPGet and TCPSocket don't really
make sense as lifecycle hooks (but I can't take that back). When we add
gRPC, it is EXPLICITLY a health check (defined by gRPC) not an arbitrary
RPC - so a probe makes sense but a hook does not.

In the future I can also see adding lifecycle hooks that don't make
sense as probes.  E.g. 'sleep' is a common lifecycle request. The only
option is `exec`, which requires having a sleep binary in your image.

* Run update scripts

pkg/kubelet/kuberuntime/kuberuntime_container_test.go

@@ -255,7 +255,7 @@ func TestLifeCycleHook(t *testing.T) {
 		},
 	}
 	cmdPostStart := &v1.Lifecycle{
-		PostStart: &v1.Handler{
+		PostStart: &v1.LifecycleHandler{
 			Exec: &v1.ExecAction{
 				Command: []string{"PostStartCMD"},
 			},
@@ -263,7 +263,7 @@ func TestLifeCycleHook(t *testing.T) {
 	}
 
 	httpLifeCycle := &v1.Lifecycle{
-		PreStop: &v1.Handler{
+		PreStop: &v1.LifecycleHandler{
 			HTTPGet: &v1.HTTPGetAction{
 				Host: "testHost.com",
 				Path: "/GracefulExit",
@@ -272,7 +272,7 @@ func TestLifeCycleHook(t *testing.T) {
 	}
 
 	cmdLifeCycle := &v1.Lifecycle{
-		PreStop: &v1.Handler{
+		PreStop: &v1.LifecycleHandler{
 			Exec: &v1.ExecAction{
 				Command: []string{"PreStopCMD"},
 			},