Add tracing spans in CRI image service and pull.go

Signed-off-by: Swagat Bora <sbora@amazon.com>

Add spans around image unpack operations
Use image.ref to denote image name and image.id for the image config digest
Add top-level spand and record errors in the CRI instrumentation service

docs/tracing.md

@@ -82,7 +82,7 @@ func clientWithTrace() error {
     defer cancel()
 
     ctx, span := tracing.StartSpan(ctx, "OPERATION NAME")
-    defer span.End()
+    defer tracing.StopSpan(span)
     ...
 }
 ```