Add support for dockerignore

[onedr0p]

Description

Hi 👋

I currently build many containers in https://github.com/home-operations/containers and for the individual apps I include a shared .dockerignore. I am looking for a way to set or override a .dockerignore via the bake GHA, maybe a inline string, or file path? Would that be something you are interested in supporting?

I would be willing to contribute the change if this is accepted.

[crazy-max]

I moved the issue to bake-action repo but I think that's someting that should be implemented on Buildx. Can you open an issue on https://github.com/docker/buildx/issues please with your use case?