Refactor: rename handler receiver from a to h to be more accurate

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What does this MR do?

Refactor: rename handler receiver from a to h to be more accurate

Closes #761 (closed)

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