Add examples of server error interceptors for Java and Kotlin

For Java, something like grpc/grpc-java#1552 (comment) .

For Kotlin, it currently has to be different: grpc/grpc-kotlin#141 (comment) .

It would also be great to mention these in the gRPC error docs: https://grpc.io/docs/guides/error/ .

[avinassh]

@mfickett would you be interested in sending a PR? (sorry for responding so late)