docs: add external passport tools for ELIXIR passport echo service
docs: add external passport tools for ELIXIR passport echo service

PiperOrigin-RevId: 332292474
Change-Id: I6c2482594c390fdd10bf4cb88add88a109953d4d

GoogleCloudPlatform/healthcare-federated-access-services,GoogleCloudPlatform/healthcare-federated-access-services,GoogleCloudPlatform/healthcare-federated-access-services,GoogleCloudPlatform/healthcare-federated-access-services