Add Metadata poll timer metric

[anbarasantr]

Fixes #46 and #49

[anbarasantr]

@seglo I am not really sure how to write tests for this scenario. Do you have any suggestion ?

[seglo]

Thanks a lot for working on this @anbarasantr. I took a quick look. The ideal way to test this would be to use the Akka typed testkit in ConsumerGroupCollectorSpec where the metric is reported. You may need to modify ConsumerGroupCollector to accept a custom java.time clock in order to control time correctly.

You could also add this to an existing or new integration test in IntegrationSpec by asserting that the metric exists and has some valid value.