Why is flat_packages enabled by default?

[jroper]

In my experience working with akka-grpc, flat_packages is almost never wanted, because there are a number of protobuf descriptors out there that are shared between many grpc interfaces, and Java versions of these very often end up on the classpath. I think scalapb made the right decision by having this feature and making the non flattened packages the default, as it avoids these issues, that often only appear at runtime. So, the question is, why does akka-grpc take the opposite approach?

[johanandren]

I don't remember at all, and the PR where we originally set it doesn't make it much clearer: #106