Add metrics to the framework

This change adds support for a metrics class which provides
the API allowing an xAPP to easily create and send a set of
measurements to a central collector for forwarding.

Issue-ID: RIC381

Signed-off-by: E. Scott Daniels <daniels@research.att.com>
Change-Id: I0926b26d4862df308ab0863260805fe057785bdc
24 files changed