async function isUsed() {
    const apiKeys = await gladys.variable.getVariables('CALLMEBOT_API_KEY', serviceId);
    return apiKeys.length > 0;
  }
@public
@description This function returns if the CallMeBot service is used.
@returns {Promise<boolean>} Returns true if the CallMeBot service is used.
@example
const used = await gladys.services.callmebot.isUsed();