examples: encryption

[dfawley]

Show TLS and ALTS examples
Good to have: mTLS example and using system CA store rather than user supplied file.
Some code example on grpc.io: https://grpc.io/docs/guides/auth.html
Java ALTS example: https://github.com/grpc/grpc-java/tree/master/examples/src/main/java/io/grpc/examples/alts
Java TLS example:https://github.com/grpc/grpc-java/tree/master/examples/src/main/java/io/grpc/examples/helloworldtls