WIP: Display the username and email of the creator of a project in the webhook data

Opening this merge request to get feedback on the change will update tests/documentation later.

What does this MR do?

Adds extra fields about the creator of a project in the system webhook sent on projects events.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Fixes the feature request #35597 (moved)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

#35597 (moved)