Add a new "Session" Authentication type

[Badgerati]

Describe the Change

A new special "Session" authentication type should be added, where the authentication simply expects a Session to be present otherwise a 401, or redirect to login, is returned.

This will help with scenarios where you want either Form, or AzureAD, or Basic authentication - and the user can pick the one they want to use. In this scenario, you'd have 3 login routes that would trigger the appropriate authentication flow, and on success a valid Session will be set on the Request. The Routes can use the Session authentication to verify a valid session, since there's no way to check for either of the 3 above auth methods in an sensible manner - even with the new Merge-PodeAuth, because of OAuth2 redirecting.

My thinking is to just have a new Add-PodeSessionAuth (in Sessions.ps1). This will setup auth to check/grab the session from the pode.sid cookie/header, if it's not there return 401/redirect to login, and if it is present set the auth'd user object appropriately.

If sessions are in used, return a 401. If the session has not auth'd user return a 401 as well.

[Badgerati]

Changing to Add-PodeAuthSession, just so it's inline with Add-PodeAuthWindowsAd, Add-PodeAuthIIS, etc.