RFR: 8312383: Improve SSL debug log

[Prajwal Kumaraswamy]

During the time of server certificate validation, users have the flexibility to use a custom X509 Key Manager implementation by extending "X509ExtendedKeyManager.".
In such cases, printing the class name in X509Authentication.java will be helpful to trace any failure of the SSL connection due to a certificate issue.

I've tested the code by running the custom X509 manager, the default X509 manager, and passing the null key manager.
The screen shots are attached here.
[x509_screen_shot_testing.zip](https://github.com/openjdk/jdk/files/14189852/x509_screen_shot_testing.zip)

Also, the internal test runs against this fix are green

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Commit messages:
 - 8312383: Improve SSL debug log

Changes: https://git.openjdk.org/jdk/pull/17742/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17742&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8312383
  Stats: 5 lines in 1 file changed: 4 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17742.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17742/head:pull/17742

PR: https://git.openjdk.org/jdk/pull/17742