Auth: Support required endorsements in Authentication Layer

[carlosscastro]

Parity for this C# PR: microsoft/botbuilder-dotnet#2019

[carlosscastro]

This can safely wait for R7, since some things being planned may affect how we expose endorsements.

[cleemullins]

@carlosscastro, how is this coming? It been sitting for a long time...

[carlosscastro]

Planning to have a PR out for this around 12/4. The change will be small but get somewhat deep in the auth layers.