Currently the spring-grpc-core imposes an opinion on Netty.
The core module should not have an opinion, but rather the
starter enforces the opinion.
Also, makes spring-grpc-core optional in the autconfigure
module as the autoconfigure will eventually be moved into
Spring Boot and at that time everything is optional.
Signed-off-by: Chris Bono <chris.bono@gmail.com>
98d744fd6b