Support servername https option

[fholzer]

What problem are you trying to solve?

Support servername https option. This alows user to send requests to servers that don't have a proper domain name, but use a certificate with a known CN/SAN that should be verified.

Describe the feature

Tells node's tls module what domain name to expect in the certificate returned by the server. No login needs to be added to got.

To support this, the only change needed to got is to add servername: undefined to the https object of defaultInternals in options.js. Without this, the set https(value) setter throws. Maybe a string type assertion in the setter would be good too.

Checklist

• I have read the documentation and made sure this feature doesn't already exist.