Draft: POC logging field variants

What does this MR do?

In the scope of gitlab-org/quality#398, we are adding a new application setting that should be consumed by various services and change which logging field names are used when logging. This MR is a POC to verify how the setting can be consumed without or with very little performance impact on logging.

TODO

• Feature flag
  • Added feature flag:
  • This feature does not require a feature flag
• I added the Changelog trailer to the commits that need to be included in the changelog (e.g. Changelog: added)
• I added unit tests or they are not required
• I added acceptance tests or they are not required
• I added documentation (or it's not required)
• I followed code review guidelines
• I followed Go Style guidelines

Related

• Issue: gitlab#596496 (closed)
• Approach and Benchmark: gitlab#596496 (comment 3344753559)