Add support for remote authentication flows

[artmasa]

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In some scenarios we would like to create initialize workflows by allowing users to reach HTTP triggers. We need users to authenticate before reaching these endpoints and ensure they meet the authorization requirements. By enabling remote authentication the functions app can orchestrate the interaction between user and IdP to obtain the credentials.

• Add authentication middleware to support the interactions there are possible with ASP.NET Core
• Dynamically add the functions endpoints required by RemoteAuthenticationHandler in the isolated process

Thanks to @nearlyheadlessarvie for raising the question on #46