Fixes for HTTP/2 max streams per connection setting

This PR makes two changes.  One is to introduce a parameter
for the HTTP/2 setting that an api-server sends to its clients
telling them how many streams they may have concurrently open in
an HTTP/2 connection.  If left at its default value of zero,
this means to use the default in golang's HTTP/2 code (which
is currently 250).

The other change is to make the recommended options for an aggregated
api-server set this limit to 1000.  The limit of 250 is annoyingly low
for the use case of many controllers watching objects of Kinds served
by an aggregated api-server reached through the main api-server (in
its mode as a proxy for the aggregated api-server, in which it uses a
single HTTP/2 connection for all calls proxied to that aggregated
api-server).

Fixes #60042

cmd/kube-controller-manager/app/options/options_test.go

@@ -72,6 +72,7 @@ func TestAddFlags(t *testing.T) {
 		"--horizontal-pod-autoscaler-downscale-delay=2m",
 		"--horizontal-pod-autoscaler-sync-period=45s",
 		"--horizontal-pod-autoscaler-upscale-delay=1m",
+		"--http2-max-streams-per-connection=47",
 		"--kube-api-burst=100",
 		"--kube-api-content-type=application/json",
 		"--kube-api-qps=50.0",
@@ -216,6 +217,7 @@ func TestAddFlags(t *testing.T) {
 					CertDirectory: "/a/b/c",
 					PairName:      "kube-controller-manager",
 				},
+				HTTP2MaxStreamsPerConnection: 47,
 			},
 			InsecureServing: &cmoptions.InsecureServingOptions{
 				BindAddress: net.ParseIP("192.168.4.10"),