Reload Netty Server's SSL Context for gRPC

I'm unsure if there are easier alternatives, but I see two potentially possible ways.

1. Make your own SslContext, mimicking DelegatingSslContext. You would swap to a different SslContext (especially during newEngine) when you want a different certificate.

2. Use a KeyManagerFactory whose key material can change over time. I'm not aware of a pre-existing implementation of such a factory, so you probably would need to implement a KeyManagerFactorySpi that delegates to a KeyManagerFactory. You could then swap out the KeyManagerFactory over time.

I will warn that it would have been easy for me to miss something that would invalidate the approaches.