Support for attesting multiple container images in a pipeline

[DavidTurner-N]

Using https://github.com/docker/bake-action and https://docs.docker.com/build/bake/ it is possible to build multiple container images in a single pipeline execution.

I have a pipeline where I am building dozens of images and would like to be able to attest them but it looks like i would have to run a matrix based approach which would consume many runners and isn't very efficient use of our self hosted runners, it would be ideal if i can pass a list of images & digests to attest.

[TateGunning]

@davidturner hope you are well. it was acting like it would support..

[lts-rad]

+1