message: docs: update backend-to-backend auth docs to reflect new TokenManager api
diff: @@ -60,12 +60,9 @@ const response = await fetch(pluginBackendApiUrl, {
  });
  ```
  -You can use the same `tokenManager` to validate tokens supplied on incoming
  +You can use the same `tokenManager` to authenticate tokens supplied on incoming
  requests:
  ```typescript
  -const isValidServerToken = await tokenManager.validateToken(token);
  -if (!isValidServerToken) {
  - throw new UnauthorizedError();
  -}
  +await tokenManager.authenticate(token); // throws if token is invalid
  ```
  