docker save to show tar download updates

[tiero]

Currently, the percentage doesn't reflect the real state of the download, It's a hacky solution for now.
the best approach would be to move to download the image as tar.gz via the docker save command.

We may need to check what the native SDK of Pythong allows to monitor the advancement of the file download, otherwise, we can check the file size on disk by checking polling the size.

Consider using SSE (Server Side Events to use EventSource browser API) but would be helpful to make sure that if a browser client re-connects to the same image download request, it keeps downloading in the background and return the updated progress.

[tiero]

This should replace the current endpoint that does not track well the download percentage

[msanjeevkumar]

I can fix the current endpoint to track the download percentage, my implementation monitors the progress of docker pull image layers and determine the average progress of all layers currently getting downloaded

[msanjeevkumar]

@tiero please review #82

[tiero]

It turns out it's not stable enough, plus is best to keep the state of the progression

[tiero]

Need to re-open as it seems to not be reliable still
bit-gpt/app#357