doc: add telemetry how-to

This patch adds all documentation for telemetry.

A description on how to use the Telemetry API with a DPDK
application is given in this document.

It also adds a release notes update for telemetry.

Signed-off-by: Ciara Power <ciara.power@intel.com>
Signed-off-by: Brian Archbold <brian.archbold@intel.com>
Signed-off-by: Kevin Laatz <kevin.laatz@intel.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>
Acked-by: Marko Kovacevic <marko.kovacevic@intel.com>