ci(ifx_package_core): pre-install imgtool signing deps for kit_pse84_ai

[IFX-Anusha]

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Description

Problem

kit_pse84_ai's build fails at the final imgtool-signing post-build step
with ModuleNotFoundError: No module named 'cryptography'.

History: how this was handled before the branch split

On pre-branch-split-main, this exact problem was solved with a Zephyr
source patch (0002-soc-infineon-pse84-install-imgtool-python-deps.patch,
applied via apply_zephyr_patches.sh) that added a pip-install
execute_process() block directly into hal_infineon's
pse84_metadata.cmake, so the dependencies got installed at CMake
configure time.

That patch mechanism isn't available on this branch structure by design
(patches touch Zephyr/HAL source under west-managed modules, which we
intentionally avoid modifying in-tree to keep sync/rebase simple). We
also confirmed via a debug CI run that the version of pse84_metadata.cmake
actually pinned by this branch's west.yml manifest doesn't contain any
pip-install logic at all yet — so the old patch's approach isn't currently
applicable here regardless.

This fix

Pre-install the same 5 packages (cryptography, cbor2, click,
intelhex, Pillow) as an explicit workflow step, scoped to
kit_pse84_ai only, right before the board build runs. This is
deliberately NOT a patch and NOT a change to bootstrap.sh (which would
install these unconditionally for every board, forever) — it's the
smallest, most scoped fix: one board, one workflow, no shared-file/HAL
changes, zero rebase-risk.

This is a temporary workaround, not the real fix

The correct long-term fix belongs upstream, in one of:

• hal_infineon's pse84_metadata.cmake itself reliably installing its own
  imgtool dependencies at CMake-configure time (it already attempts this
  in newer HAL revisions, but only via message(WARNING ...) on failure,
  which lets the build proceed and fail later with a confusing error
  instead of aborting cleanly).
• Or better: mcuboot's Python requirements (cryptography, cbor2, etc.)
  being installed as part of Zephyr's own standard workspace bootstrap
  (requirements-base.txt), the same way every other Zephyr board that
  signs images with imgtool is expected to have pip3 install imgtool
  run manually beforehand — this is literally called out as a TODO in the
  current pse84_metadata.cmake source: "Remove once mcuboot's Python
  requirements are installed as part of the standard Zephyr workspace
  setup."

Until either of those lands upstream in the HAL/Zephyr modules we
consume, this workflow-level pre-install keeps our CI green without
depending on unreliable, warning-only auto-install logic living in a
module we don't control.