fix: improve conversion of image config to Dockerfile

[nikpivkin]

Description

This PR includes the following changes:

• extracts config conversion to dockerfile into a separate function to facilitate testing
• adds support for buildkit metadata instructions, e.g. env, arg. Such commands show up in the history without the # buildkit suffix, so Trivy ignored them.

ENTRYPOINT ["/bin/sh" "-c" "echo test"]
RUN /bin/sh -c apk add $pkg # buildkit

• fixes the handling of run with build arguments

Related issues

• Close bug: docker history analyzer exports instructions with build arguments without processing #8277

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).

[knqyf263]

Are there any checks that need to evaluate variables? Does RUN apk add $pkg work with all checks?

[nikpivkin]

Many checks will not need to evaluate arguments.

[knqyf263]

LGTM. I would wait for @DmitriyLewen's review.

[DmitriyLewen]

LGTM