Send billing_project for every request when set (#5086) (#769)

Signed-off-by: Modular Magician <magic-modules@google.com>

google/config.go

@@ -368,6 +368,7 @@ func (c *Config) LoadAndValidate(ctx context.Context) error {
 	if err != nil {
 		return err
 	}
+
 	// Userinfo is fetched before request logging is enabled to reduce additional noise.
 	err = c.logGoogleIdentities()
 	if err != nil {
@@ -390,6 +391,12 @@ func (c *Config) LoadAndValidate(ctx context.Context) error {
 		headerTransport.Set("X-Goog-Request-Reason", c.RequestReason)
 	}
 
+	// Ensure $userProject is set for all HTTP requests using the client if specified by the provider config
+	// See https://cloud.google.com/apis/docs/system-parameters
+	if c.UserProjectOverride && c.BillingProject != "" {
+		headerTransport.Set("X-Goog-User-Project", c.BillingProject)
+	}
+
 	// Set final transport value.
 	client.Transport = headerTransport