Timer metric type

[kennknowles]

Add support for Timer metric type to the SDK.
Interface should be along the lines of:

void update(Duration duration);
<T> T time(Callable<T>  event);
Closeable time();

Compare to http://metrics.dropwizard.io/3.1.0/apidocs/com/codahale/metrics/Timer.html

Could reuse code for this and https://issues.apache.org/jira/browse/BEAM-1613

Imported from Jira BEAM-1699. Original Jira may contain additional context.
Reported by: aviemzur.

[kennknowles]

The following subtask(s) are associated with this issue: #18333, #18334