op-mode: T6400: pki: unable to generate fingerprint for ACME issued certificates (backport #3518)

[mergify]

Change Summary

This fixes (for and ACME generated certificate)

vyos@vyos:~$ show pki certificate vyos fingerprint sha512 Traceback (most recent call last):
  File "/usr/libexec/vyos/op_mode/pki.py", line 1081, in <module>
    show_certificate_fingerprint(args.certificate, args.fingerprint)
  File "/usr/libexec/vyos/op_mode/pki.py", line 934, in show_certificate_fingerprint
    print(get_certificate_fingerprint(cert, hash))
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3/dist-packages/vyos/pki.py", line 76, in get_certificate_fingerprint
    fp = cert.fingerprint(hash_algorithm)
         ^^^^^^^^^^^^^^^^
AttributeError: 'bool' object has no attribute 'fingerprint'

After the fix:

vyos@vyos# run show pki certificate vyos fingerprint sha256 10:2C:EF:2C:DA:7A:EE:C6:D7:8E:53:12:F0:F5:DE:B9:E9:D0:6C:B4:49:1C:8B:70:2B:D9:AF:FC:9B:75:A3:D2

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T6400

Related PR(s)

Component(s) name

PKI op-mode

Proposed changes

How to test

vyos@vyos:~$ show pki certificate vyos fingerprint sha256 

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

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This is an automatic backport of pull request #3518 done by [Mergify](https://mergify.com).