code: public AddonChange addAddon(String appName, String addonName) {
          return connection.execute(new AddonInstall(appName, addonName), apiKey);
      }
docs: Add an addon to the app.
  @param appName App name. See {@link #listApps} for a list of apps that can be used.
  @param addonName Addon name. See {@link #listAllAddons} to get a list of addons that can be used.
  @return The request object