Liveness endpoint should return non-empty JSON object

[lycarter]

What happened?

Java witchcraft has diverged from the SLS spec and returns a simple "alive" for the liveness endpoint. Consuming services now expect that, while witchcraft-go returns an empty JSON object, which results in some consuming services not considering witchcraft-go services "live"

What did you want to happen?

Witchcraft-go should follow the lead of Java witchcraft and return a non-empty JSON response on the liveness endpoint

(feel free to reach out internally for more context - Lilliput#360)