Disabling AAD Authentication from R2 Services

Context and Scope

With the Introduction of Istio to the Azure Platform, Authentication will be done at Istio Proxy. So AAD authentication will be disabled.

To make it backward compatible, In R2 services AAD authentication will be Disabled Using "azure_istioauth_enabled" env variable.

In Entitlement Service New Authentication Filter will be Introduced to decode payload coming from Istio proxy and set security context which is required for Authorization.