Drop Armeria and switch back to vanilla netty

[ptrthomas]

Armeria was expected to help support formats like gRPC etc. but it turns out that library based extensions was a better approach.

switching back to netty would keep dependencies simpler, and bring back HTTPS support for mocks which a few teams are missing

example of need for HTTPS support here: https://github.com/viclovsky/swagger-coverage/blob/master/swagger-coverage-karate/README.md#-the-problem-with-https-and-the-workaround

the thread referred: #640