New metrics registry for micrometer

At the moment only Dropwizard/Yammer metrics are provided.

A new plugin for Micrometer metrics would be a nice to have. However, I think this should reside in a separate project. Not sure if there is any plans to include something like an official project for this, perhaps in https://github.com/pinot-contrib

I'll try to take this discussion to the chat, for now I'll raise this issue.

No files, tests, or entry points are named. Start by reviewing the existing Dropwizard/Yammer metrics support and the pinot-contrib project, then determine whether Micrometer belongs in a separate plugin; done requires an agreed project location and scope.

Written by the indexing model from the issue text.