CEP 44: Use underscore-separated field names

[jaimergp]

Checklist for submitter

• I am submitting a new CEP: Put your title here.
  • I am using the CEP template by creating a copy cep-0000.md named cep-XXXX.md in the root level.
• I am submitting modifications to CEP 44.
  • The PR title reflects the CEP I'm modifying: CEP XX: Amend XYZ.
  • I updated the "Updated" date.
  • I added the link of this PR to the Discussions row.
  • I added or extended the ## Changelog section right above the final "Copyright" section with an item that uses syntax YYYY-MM-DD: Brief explanation of changes.
• Something else: (add your description here).

Comes from discussion at #146 (comment)

[wolfv]

Thanks