Implement gssapi-with-mic user authentication with Kerberos

[scott-xu]

This PR adds support for gssapi-with-mic user authentication with Kerberos which is defined at https://datatracker.ietf.org/doc/html/rfc4462.

Close #780
Close #170
Close #114

[scott-xu]

This PR is primarily based on tmds/Tmds.Ssh#188. Credits to @jborean93 and @tmds

🎏 Call for help!
This PR is still at early stage. If someone can help implement ReflectedNegotiateContext or add integration test, that would be great!

[Rob-Hague]

Some high-level questions

1. I am not excited by the prospect of reflection/UnsafeAccessor. Is it just for lower targets? If so, I would prefer to restrict it to targets where it is possible via public api (NET 9+ presumably).

2. It seems like it would be easier to just have:

public class GssApiAuthenticationMethod(NegotiateAuthenticationClientOptions options)
{ }

as the public api?

3. Have you thought about how to test it? Presumably something can be set up via the dockerfile

[scott-xu]

1. I am not excited by the prospect of reflection/UnsafeAccessor. Is it just for lower targets? If so, I would prefer to restrict it to targets where it is possible via public api (NET 9+ presumably).

Reflection is to support .NET Framework.
UnsafeAccessor is to support .NET 8.0

One reason to choose SSH.NET is that it supports lower targets.

2. It seems like it would be easier to just have:

public class GssApiAuthenticationMethod(NegotiateAuthenticationClientOptions options)
{ }

as the public api?

There are too many options than needed if we use NegotiateAuthenticationClientOptions as public API.

3. Have you thought about how to test it? Presumably something can be set up via the dockerfile

That's the "call out for help" item 😄