add handler for new discovery endpoint so that CLI tools like bq work (…

…#8)

Related: 

- Issue in the upstream repo: goccy#290
- PR in the upstream repo: goccy#338

server/handler.go

@@ -54,8 +54,9 @@ func encodeResponse(ctx context.Context, w http.ResponseWriter, response interfa
 }
 
 const (
-	discoveryAPIEndpoint = "/discovery/v1/apis/bigquery/v2/rest"
-	uploadAPIEndpoint    = "/upload/bigquery/v2/projects/{projectId}/jobs"
+	discoveryAPIEndpoint    = "/discovery/v1/apis/bigquery/v2/rest"
+	newDiscoveryAPIEndpoint = "/$discovery/rest"
+	uploadAPIEndpoint       = "/upload/bigquery/v2/projects/{projectId}/jobs"
 )
 
 //go:embed resources/discovery.json

server/server.go

@@ -79,6 +79,7 @@ func New(storage Storage) (*Server, error) {
 		r.Handle(fmt.Sprintf("/bigquery/v2%s", handler.Path), handler.Handler).Methods(handler.HTTPMethod)
 	}
 	r.Handle(discoveryAPIEndpoint, newDiscoveryHandler(server)).Methods("GET")
+	r.Handle(newDiscoveryAPIEndpoint, newDiscoveryHandler(server)).Methods("GET")
 	r.Handle(uploadAPIEndpoint, &uploadHandler{}).Methods("POST")
 	r.Handle(uploadAPIEndpoint, &uploadContentHandler{}).Methods("PUT")
 	r.PathPrefix("/").Handler(&defaultHandler{})