Support TLS 1.3 [API-1920] #801
Description
Although .NET supports (at least in some versions) the SslProtocols.Tls13 enumeration value, we explicitly reject it in SslOptions. We should support it wherever it is supported.
Note that ... it is supported by .NET Framework 4.8 but not by NetStandard, meaning that we may have to ship a net48 build of the client in addition to the netstandard-2.0 one, and ensure that the correct build is selected.