eShopOnContainers updated to .NET Core 3.0!

[mvelosop]

eShopOnContainers has been updated to .NET Core 3.0!

Highlights

• Update to .NET Core 3.0
• Use of gRPC for microservice-to-microservice communication
• Use of Envoy Proxy for BFF
• Repo cleanup (simpler README and folder structure)
• Initial Service Mesh support (Linkerd)

Get more details in the release notes or dive right into the repo