sdk: enable xz RPM payload support in the SDK

[jiria]

Azure Linux 4 ships xz-compressed RPM payloads, which the SDK's rpm cannot install because it is built without the lzma USE flag (it never advertises rpmlib(PayloadIsXz)).

• Add app-arch/rpm caps lzma bzip2 to the SDK target profile (profiles/coreos/targets/sdk/package.use).
• Putting it in the profile rather than in Dockerfile.sdk-update means it applies both when a fresh SDK image is bootstrapped and when an existing one is updated — the existing --changed-use emerge in Dockerfile.sdk-update picks up the rebuild.
• bzip2 covers rpmlib(PayloadIsBzip2); caps is pinned because file capabilities from Azure Linux packages depend on it.

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Work item: AB#22734

[Copilot]

Pull request overview

Enables the Gentoo app-arch/rpm features required for the SDK to install Azure Linux 4 RPMs that use xz-compressed payloads, by setting the appropriate USE flags in the SDK target profile.

Changes:

• Enable lzma and bzip2 USE flags for app-arch/rpm so it advertises/handles rpmlib(PayloadIsXz) and rpmlib(PayloadIsBzip2).
• Enable caps USE flag for app-arch/rpm to support applying file capabilities from Azure Linux packages.

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[jiria]

Validation

Built the SDK two ways from this branch and inspected the resulting containers.

Baseline (without this change):

rpmlib(PayloadIsBzip2) = 3.0.5-1
rpmlib(PayloadIsZstd)  = 5.4.18-1

With this change — SDK update path (update_chroot + Dockerfile.sdk-update):

rpmlib(PayloadIsBzip2) = 3.0.5-1
rpmlib(PayloadIsLzma)  = 4.4.2-1
rpmlib(PayloadIsXz)    = 5.2-1
rpmlib(PayloadIsZstd)  = 5.4.18-1

With this change — from-scratch bootstrap path (catalyst):

rpmlib(PayloadIsBzip2) = 3.0.5-1
rpmlib(PayloadIsLzma)  = 4.4.2-1
rpmlib(PayloadIsXz)    = 5.2-1
rpmlib(PayloadIsZstd)  = 5.4.18-1

The emerge output confirms app-arch/rpm is rebuilt with the expected flags:

[ebuild  N     ] app-arch/rpm-4.20.1-r2::portage-stable
  USE="acl bzip2 caps iconv lzma python readline sequoia sqlite zstd
       -audit -berkdb -dbus -doc (-nls) -openmp -selinux"

Both paths resolve the same profile via get_sdk_profile()
(build_library/toolchain_util.sh), which is consumed by update_chroot and
by DEFAULT_PROFILE in build_library/catalyst.sh — so a single
profiles/coreos/targets/sdk/package.use entry covers both, and no
Dockerfile change is needed.