Follow-up from "Added a UI to create timelogs" - Refactor issuable helper fields to snake_case

The following discussion from !101563 (merged) should be addressed:

• @mparuszewski started a discussion: (+1 comment)

  question (non-blocking): I know that you are following what we already have in this method, but should we create a follow-up issue to rename all keys to be snake_cased? I believe when this helper method is used in the view, it will automatically be accessible for Vue app with camelCase anyway? 🤔