Add SteamAuthentication to handle new Steam login flow sessions

[xPaw]

Fixes #1125.

This is a work in progress. When beginning an auth session it returns a new object which some methods to do stuff on the session.

It adds a new IAuthenticator class to provide 2FA codes (with an example implementation that just reads from the console).

What I am not entirely certain about is the polling design (right now it's just a loop with task.delay).

[xPaw]

Logging in as SteamClient requires to do it over CM. I tried over webapi, but it throws InvalidParam, and using other types will give InvalidPassword when trying to logon.

This means that CM will kick you in 60 seconds if you don't auth. Steam client also has this issue, but it will reconnect and just continue polling.

I don't want to deal with graceful reconnections in the scope of this PR.

[JustArchi]

I tested this implementation in ASF, works good enough in my opinion to be released as part of SK2 alpha release: JustArchiNET/ArchiSteamFarm#2843

[xPaw]

Current code should good enough to release an alpha version and get this tested by consumers. We can improve the implementation and specifics in the future.

[Adios22]

When alpha version will be available to download?

[yaakov-h]

I'd be tempted to pull in System.IdentityModel.Tokens.Jwt instead.

[xPaw]

I tried it for a minute, and getting info out of it is more effort than I'm willing to spend.

[yaakov-h]

There are also still obsoletion warnings in the build that need to be taken care of (probably just suppressed).