[8.13](backport #39663) Style fixes for Buildkite xpack/auditbeat pipeline

[mergify]

Proposed commit message

Fixed x-pack/auditbeat pipeline agent, step and notification naming according to general standard.
Should be backported to 8.13 and 8.14 branches only since 7.17 styling is fixed within #39658

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in CHANGELOG.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Author's Checklist

• .buildkite/x-pack/pipeline.xpack.auditbeat.yml

Related issues

• Relates: https://github.com/elastic/ingest-dev/issues/3254

Logs

BK builds: https://buildkite.com/elastic/beats-xpack-auditbeat/builds?branch=elastic%3Amergify%2Fbp%2F8.13%2Fpr-39663

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This is an automatic backport of pull request #39663 done by [Mergify](https://mergify.com).