FR: an option to delay `--cache-to` pushes

Description

Hello
I am doing many successive build calls, each often reusing just-built stages. Today, using --cache-to on each build call incurs an often-remote push that slows down my calls.

I would like to be able to delay pushes to registry caches and to introduce some command to push the caches after these builds. I use registry caches but this may also be useful for GHA or S3 or other cache backends.

I’m thinking a CSV option to --cache-to could be a push=false. E.g.

--cache-to type=registry,ref=myregistry.com/myslug/myimage:mytag,mode=max,push=false

The command to use to push should take filtering parameters in (like image or image and tag). E.g.

docker buildx cache push --ref=myregistry.com/myslug/myimage

A flag should allow to periodically check for new things to upload, this way the command can be run concurrently to the build calls and terminate after a set time.

docker buildx cache push --ref=myregistry.com/myslug/myimage --wait-for 5s &

Could this command be a simple registry syncing client? Or maybe the caching system is more complex than that?

This seems related: https://github.com/docker/buildx/issues/537

Have a nice day

Start by tracing the existing --cache-to handling and the docker buildx cache command entry points, then read the related issue #537. The request spans delayed uploads, a cache push command, filtering, waiting, and multiple backends; done would require an agreed design and documented behavior for those cases.