Benchmark the `Images` implementation (image list) against an image
store with 10, 100 and 1000 random images. Currently the images are
single-platform only.
The images are generated randomly, but a fixed seed is used so the
actual testing data will be the same across different executions.
Because the content store is not a real containerd image store but a
local implementation, a small delay (500us) is added to each content
store method call. This is to simulate a real-world usage where each
containerd client call requires a gRPC call.
Signed-off-by: Paweł Gronowski <pawel.gronowski@docker.com>