Add a plugin for service discovery.

[pith]

Here is some ideas: dropwizard-discovery

1. Register/Unregister a Nuun application as a service on application lifecycle.

2. Provide an API to consume services

[ejemba]

I think this can be using the Kernel Extension mechanism. I create an issue to explain it.

[ejemba]

@pith This can be included in the nuun-cloud work, where we clearly address those issues.

[pith]

I think we should move this issue. A meta repo include all the Nuun plugins via git submodules could be an idea.