* Remove unnecessary IR graph loggings.

* Add the guides for protecting sensitive info leaking in the logs.

  `CONTRIBUTING.md` now contains the guide to prevent sensitive info leaking in the debug logs.

  Fixes: #14778
  Pull-request: #14779

* Add sample source codes to the `CONTRIBUTING.md`.

* Apply suggestions from code review

Contribution guide for using sensitive data in Logstash improved.

Co-authored-by: João Duarte <jsvd@users.noreply.github.com>

Co-authored-by: João Duarte <jsvd@users.noreply.github.com>