Hide authentication section until we implement configuration passing

Currently ReDoc shows the "Authentication" section by default. You can disable it by setting the no-auto-auth attribute:

    $build = [
      '#theme' => 'redoc',
      '#attributes' => [
        'no-auto-auth' => TRUE,
      ],
      '#openapi_url' => …,
    ];

… but that's just a work-around until we can surface the authentication information automatically.

See https://rebilly.github.io/ReDoc/#section/Authentication for an example.

The next phase of this depends on #2987434: Support config passing to allow injection of Authentication data..