TCK: add micrometer section to TCK

[donbourne]

A micrometer section of the TCK should test:

• that the prometheus-formatted output for each of the metric types looks exactly as expected for micrometer-based implementations

Note that the micrometer section should be in addition to the common section of the TCK. The common section of the TCK can be assumed to already be testing things that all implementations are expected to do.

[donbourne]

rather than build tests specifically for micrometer, plan is to have tests that work for both an existing impl's prometheus output and for micrometer's PrometheusMeterRegistry.scrape output as described in #693