function applyZenkoUserMD(metaHeaders) {
    if (process.env.REMOTE_MANAGEMENT_DISABLE === '0' &&
        !metaHeaders[zenkoIDHeader]) {
        // eslint-disable-next-line no-param-reassign
        metaHeaders[zenkoIDHeader] = _config.getPublicInstanceId();
    }
}
applyZenkoUserMD - if request is within a Zenko deployment, apply user
metadata called "zenko-source" to the object
@param {Object} metaHeaders - user metadata object
@return {undefined}