Add support for PKCS#12 server certs

[dmercuriali]

Currently you can pass an sslCertFile and a sslChainCertFile, the first can be password protected but the chain must be plain.

Some companies policy requires every cert file to be password protected so we should provide some kind of support.
We could add support for the chain in the PKCS#12 format, but netty doesn't seem to natively support it in the SslContextBuilder creation. We should probably provide our own KeyManager