[CAP] Check if User exists in SuccessFactors

To check if a record exists, you can simply use the HEAD query.

“HEAD is almost identical to GET, but without the response body.” (https://www.w3schools.com/tags/ref_httpmethods.asp)

Unfortunately, there is no shortcut in CAP for a HEAD query, so simply use send with method HEAD.

    sfsfSrv = await cds.connect.to('sfsf')

    try {
        await sfsfSrv.send('HEAD', `/User('${userId}')`)
        return true  // status 200
    } catch (err) {
        return false // status 404
    }