ENG-87659 - convert blobs to zstd from gzip before push

[narasul]

10% to 35% pull time improvement on some images, depending on cluster(how good network is).

What changed:

• if buildx is available create a buildkit builder
• jig build builds the image with zstd compression instead of default gzip
• jig push pushes the image that was built with the the buildkit
• jig deploy builds the image with buildx and directly pushes to registry(won't be locally available if not pulled)
• --warmup flag makes builds fallback to default gzip build(it is possible to make it work with buildx but that's future work if we want to make it nicely)

(I need to clean up the code but please comment on the flow, see if I missed an edge case or two)

[mintlify]

Docs PR opened: https://github.com/togethercomputer/mintlify-docs/pull/847

Added a tip to the jig push CLI reference documenting the new Buildx + zstd push behavior and gzip fallback.