Allow registry clients to connect via http2

Http2 will be enabled by default and can be disabled with a configuration option.

Signed-off-by: Adam Duke <adam.v.duke@gmail.com>

configuration/configuration_test.go

@@ -82,6 +82,9 @@ var configStruct = Configuration{
 		Debug   struct {
 			Addr string `yaml:"addr,omitempty"`
 		} `yaml:"debug,omitempty"`
+		HTTP2 struct {
+			Disabled bool `yaml:"disabled,omitempty"`
+		} `yaml:"http2,omitempty"`
 	}{
 		TLS: struct {
 			Certificate string   `yaml:"certificate,omitempty"`
@@ -97,6 +100,11 @@ var configStruct = Configuration{
 		Headers: http.Header{
 			"X-Content-Type-Options": []string{"nosniff"},
 		},
+		HTTP2: struct {
+			Disabled bool `yaml:"disabled,omitempty"`
+		}{
+			Disabled: false,
+		},
 	},
 }