Support unpacking Docker images

[ben-z]

This PR introduces the unpack URL param to unpack uploaded packages using https://github.com/WATonomous/docker-unpack . This is an alternative to #8 .

[ben-z]

cc @alexboden I deployed and tested this manually:

docker pull ghcr.io/watonomous/infra-config:master
docker save ghcr.io/watonomous/infra-config:master > /tmp/provisioner.tar

curl -XPOST --form "file=@/tmp/provisioner.tar;filename=provisioner-test-ben" 'cvmfs-ephemeral.cluster.watonomous.ca/app/repos/cvmfs-ephemeral.cluster.watonomous.ca?overwrite=true&unpack=true'

apptainer exec --writable-tmpfs --containall --fakeroot --no-home --bind ../infra-config:/infra-config:ro --bind ../infra-config/outputs:/infra-config/outputs --pwd /infra-config /cvmfs/cvmfs-ephemeral.cluster.watonomous.ca/provisioner-test-ben bash

curl took 33 seconds on thor-slurm1. After the folder appeared in /cvmfs/, starting the container took 5 seconds ish. I ran a command ./kubernetes/run.sh k9s -A, and it took about 3 seconds to show me the password prompt.

Overall I think it's going to be an improvement because we eliminate downloading and loading the docker cache, and start the container right away.

[ben-z]

A future improvement is to be able to stream uploading the file. Currently, if we do docker save ... | curl -XPOST --form "file=@-;filename=..., we get an out of memory error. This is because CURL buffers the entire stdin stream in memory before performing the request. We can change the server to support streaming the body instead of using formdata to speed this up. Then we can build and upload at the same time:

docker build ... | curl ...

Tracking this in #12