.NET Configuration section containing Hocon CDATA

- This PR introduces 3 new classes in Akka.Configuration.Hocon providing the functionality to parse a simple configuration section containing pure Hocon CDATA. I've intentionally decided to place the CFG section in that namespace, in case I attempt to come up with a pure .NET configuration (which I'd put in Akka.Configuration)

- The configuration section exposes a parsed Akka configuration via lazy loading

- Simple parsing test and example usage of the configuration section added to Akka.Tests
Do we need `""` in `CDATA`? single `"` should be enough?