hack: Rework+cleanup container build

[cgwalters]

Main motivation: I was looking at making more changes here

• Use an idiom I'd like to standardize more of copy context to FROM scratch image which is then mounted and consumed in other phases by mounting. This helps avoid polluting later containers with intermediate copied files.
• Change build.sh to handle being run from any directory
• Drop the dev-rootfs stuff as it's weird and awkward; instead we should encourage multi-step builds deriving from this image
• Don't make bootc.tar.zst only to immediately untar it; just use COPY from the build container
• Use heredocs to condense multiple RUN invocations to avoid pointless small layers

[cgwalters]

ERROR Installing to filesystem: Creating ostree deployment: Pulling: Importing: Parsing layer blob sha256:0f299f3f346782473308fd887c25d99af245027c4bf8df55ddf47121b4aa2d36: error: (null): Processing tar: Failed to commit tar: ExitStatus(unix_wait_status(256))

Humm...very confused by this failure

[henrywang]

.git was added in gitignore, so there's an error fatal: not a git repository (or any of the parent directories): .git and when we do tar -C / --zstd -xvf /tmp/bootc.tar.zst, some of files report tar: ./usr/bin/bootc: implausibly old time stamp -9223372036854775808. That might be the root cause?

[Copilot]

Pull Request Overview

This PR reworks the container build process to standardize image preparation and improve the build caching strategy. Key changes include:

• Standardizing the build script for execution from any directory.
• Refactoring the Containerfile to separate context and build stages and reduce intermediate file handling.
• Enhancing the CI workflow with updated Podman support for heredocs.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
hack/build.sh	Updated to dynamically determine its directory and adjust paths accordingly.
hack/Containerfile	Refactored multi-stage build with context and heredoc usage to reduce intermediate artifacts.
.github/workflows/ci.yml	Added a step to update Podman and related tools for improved heredoc support in CI.
.dockerignore	Updated ignore rules to manage large files and prevent cache invalidation.