api/resolver: update resolver to enable subdomain routing (#1747)

* api/resolver: update domain / service prefix usage

* api/resolver/subdomain: implement subdomain resolver for domain resolution

* api/handler: fix tests

api/handler/http/http_test.go

@@ -58,7 +58,7 @@ func testHttp(t *testing.T, path, service, ns string) {
 		router.WithHandler("http"),
 		router.WithRegistry(r),
 		router.WithResolver(vpath.NewResolver(
-			resolver.WithNamespace(resolver.StaticNamespace(ns)),
+			resolver.WithServicePrefix(ns),
 		)),
 	)