flasher: improve logging with secure boot

[jakogut]

Print the PCR digest values used to create the PCR policy used to seal the LUKS passphrase during flashing. These values can be cross referenced with the logs during secure boot to diagnose policy check failures.

Change-type: patch

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Contributor checklist

• Changes have been tested
  • Covered in automated test suite
  • Manual test case recorded
• Change-type present on at least one commit
• Signed-off-by is present
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[github-actions]

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[jakogut]

@balena-ci I self-certify!