Guidance on using different Micrometer Registries

[jgallimore]

SmallRye Metrics provides the ability to use other backends, besides the Prometheus registry. The other registries are push-based, so SmallRye will push metric data to other systems, such as Elastic or Graphite at a defined interval.

It would be useful to provide some example setups and configurations for some of these other registries, to enable users to get started more easily.

[donbourne]

@jgallimore , this would still be a really cool thing to have (poke, poke) :-)