Y16 format enablement for external provider

added Y16 (depth) support for the external provider.
refactored initOutputCharsKeys to support both depth and color metadata according to the connected camera.
the VTS changes will be pushed to pie-vts-dev

Test: tested on intel depth camera D415 manually in addition to the VTS tests.

Change-Id: I358686e7c4330bb180dec4a9cce3bc1cf5475260
Merged-In: I358686e7c4330bb180dec4a9cce3bc1cf5475260
Signed-off-by: Emil Jahshan <emil.jahshan@intel.com>