The OpenMetrics specification has been released (finalized?) and now the Prometheus Java client uses the OpenMetrics data model since 0.10.0. We are already on that version in the master branch now, which required #2418 to compile. This issue is to track other changes that should/could be made in support of OpenMetrics.

• Units (deferred to Support OpenMetrics Unit #2482)
• Support multiple scraping formats (Prom and OpenMetrics text format) OpenMetrics scrape support #2486
• _created timestamp (does Prometheus server even do anything with these currently?)

Note: Experimental support for OpenMetrics scrape format was added to Prometheus 2.5.0.