Adds support for image pull per runtime
class with the help of gc labels.
The image pull code path remains the same
but during UpdateImage() call, the image index
or manifest is walked to find the appropriate
platform, snapshot the image was unpacked for.
If such a match if found, find all matching
runtime handlers with identical platform and
snapshotter from CriConfig.RuntimePlatforms and
update containerd and cri image stores appropriately.
New entry for tuple (ref,runtimehandler) are made in
containerd metadata store and snapshot gc labels are
added to take reference on unpacked snapshot.
Further, image gc labels are also added to the root image
to ensure appropriate resource cleanup.
This approach also makes the image delete and reload code
paths simple.

Signed-off-by: Kirtana Ashok <kiashok@microsoft.com>

Signed-off-by: Kirtana Ashok <kiashok@microsoft.com>

Signed-off-by: Kirtana Ashok <kiashok@microsoft.com>