message: show how to use config when setting up api
  Most API will require some configuration.
  So it would be more useful to show an example where the config is available when the API's are being wired up
diff: @@ -71,8 +71,11 @@ import {
  AlertApiForwarder,
  ErrorApiForwarder,
  ErrorAlerter,
  + ConfigApi
  } from '@backstage/core';
  +
  +const apis = (config: ConfigApi) => {
  const builder = ApiRegistry.builder();
  // The alert API is a self-contained implementation that shows alerts to the user.
  @@ -80,9 +83,11 @@ const alertApi = builder.add(alertApiRef, new AlertApiForwarder());
  // The error API uses the alert API to send error notifications to the user.
  builder.add(errorApiRef, new ErrorAlerter(alertApi, new ErrorApiForwarder()));
  + return builder.build();
  +}
  const app = createApp({
  - apis: apiBuilder.build(),
  + apis,
  // ... other config
  });
  ```
  