function getAmzRestoreResHeader(objMD) {
    if (objMD.archive &&
        objMD.archive.restoreRequestedAt &&
        !objMD.archive.restoreCompletedAt) {
        // Avoid race condition by relying on the `archive` MD of the object
        // and return the right header after a RESTORE request.
        // eslint-disable-next-line
        return `ongoing-request="true"`;
    }
    if (objMD['x-amz-restore']) {
        if (objMD['x-amz-restore']['expiry-date']) {
            const utcDateTime = new Date(objMD['x-amz-restore']['expiry-date']).toUTCString();
            return `ongoing-request="${objMD['x-amz-restore']['ongoing-request']}", expiry-date="${utcDateTime}"`;
        }
    }
    return undefined;
}
Get response header "x-amz-restore"
Be called by objectHead.js
@param {object} objMD - object's metadata
@returns {string|undefined} x-amz-restore