VAULT-31594 Add debug level logging to the LDAP auth library

[JMGoldsmith]

Description

What does this PR do?

This PR updates the LDAP authentication to use debug level logging. After the introduction of the CAP library the debug logging was removed. This PR adds it back.

TODO only if you're a HashiCorp employee

• [x ] Backport Labels: If this PR is in the ENT repo and needs to be backported, backport
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  • If this fixes a critical security vulnerability or severity 1 bug, it will also need to be backported to the current LTS versions of Vault. To ensure this, use all available enterprise labels.
• ENT Breakage: If this PR either 1) removes a public function OR 2) changes the signature
  of a public function, even if that change is in a CE file, double check that
  applying the patch for this PR to the ENT repo and running tests doesn't
  break any tests. Sometimes ENT only tests rely on public functions in CE
  files.
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[github-actions]

CI Results:
All Go tests succeeded! ✅

[github-actions]

Build Results:
All builds succeeded! ✅

[fairclothjm]

LGTM! Thanks!

One comment that is not blocking: I think the IsDebug checks are unnecessary. No need to remove them now. But in the future we probably only need to do this when we are calculating a value in a hot path for requests.

[fairclothjm]

I added the backport/1.18.x label since that one was missing