dnsdist: add support for password protected PCKS12 files for TLS configuration

[chbruyand]

Short description

This adds support for password protected PCKS12 files. addDOHLocal and addTLSLocal now accept either a single cert parameter (without any key) and thus try to open it as a PCKS12 file or directly a TLSCertificate object initialized via newTLSCertificate.

Checklist

I have:

• read the CONTRIBUTING.md document
• compiled this code
• tested this code
• included documentation (including possible behaviour changes)
• documented the code
• added or modified regression test(s)
• added or modified unit test(s)

[rgacogne]

Code looks good! A regression test creating a password-protected PKCS12 file in runtests then loading it in test_DOH and/or test_TLS would be nice :)

[rgacogne]

Test failures are unrelated:

• rec regression (ubsan+asan):

FAIL: testNotify (test_Notify.NotifyRecursorTest)
  ----------------------------------------------------------------------
  Traceback (most recent call last):
    File "/home/runner/work/pdns/pdns/regression-tests.recursor-dnssec/test_Notify.py", line 117, in testNotify
      self.checkRecordCacheMetrics(4, 2)
    File "/home/runner/work/pdns/pdns/regression-tests.recursor-dnssec/test_Notify.py", line 64, in checkRecordCacheMetrics
      self.assertEqual(int(entry['value']), expectedHits)
  AssertionError: 3 != 4

• test-recursor-bulk:

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context deadline exceeded

[rgacogne]

Eww, using the GH editor to fix a conflict in the documentation resulted in a big merge commit. @chbruyand Shall I rebase your branch on master instead?

[chbruyand]

Rebased to fix conflict