Breaking changes

When creating a legacy boot image, grub2-install must now be installed in the target OS.
- For Azure Linux 2.0 and 3.0, if grub2-install isn't installed in the target OS, then Image Customizer will fall back to using grub2-install from the build host / container. But this behavior is deprecated.
Removed the run.sh script from the container. This script has been deprecated for a few releases now, in favor of the newer OCI image API.

Breaking changes for preview features

Removed all existing distro preview feature flags and replaced them with a single preview-distro-version for all preview distros and distro versions.
For create subcommand, change --tools-file to --tools-dir.
Placed --tools-dir under its own preview feature flag.

Added a new unsupported-distro-version preview feature flag that allows customizing unrecognized distro versions.
Add support for --tools-dir CLI parameter to customize subcommand. This is used by Image Customizer to do package operations without needing the package manager commands (e.g. tdnf, dnf, rpm, apt-get, dpkg-query, etc.) to be installed in the target OS.
- Note: Not all package operations use --tools-dir yet.

Add --setfiles-context CLI parameter, to help with customizing an AZL3 image on a AZL4 or Fedora build machine with SELinux enabled.

Lots of dependency version bumps.
Fix issue where GPG keys are not auto-imported by tdnf when downloading package repo metadata.
When generating LiveOS ISO or PXE image, properly detect kernel files, particularly when custom kernel packages are being used.
Allow ACL image to be mounted as read-only.
When converting ACL image to COSI image format, don't fail if package list collection fails.
Remove requirement to bind-mount /dev when running Image Customizer container. Now the container's entrypoint will automatically create a devtmpfs mount over its /dev directory.
Report package snapshot time API as unsupported for Ubuntu and AZL4.
Fix name of os.bootloader.resetType in some error messages.
Various fixes that will eventually enable creation of AZL4 LiveOS ISO and PXE images:
- Make package information retrieval distro aware.
- Make bootloader file paths distro aware.
- Preserve symlinks when creating LiveOS images.
For AZL4, when hard-resetting the bootloader config, set the grub timeout to 1s to match AZL4 defaults.

Added doc on the kernel modules that Image Customizer requires.
Added GitHub issue template.
Fix supported features list for Azure Linux 4.0.
Document the /_imageconfigs mount directory that exists when user scripts are running.