Issue created at docs

What does this MR do?

Clarifies created_at for creating issues via the API.

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

No.

Why was this MR needed?

Docs were unclear.

What are the relevant issue numbers?

Closes #18458 (closed) and closes #19863 (closed).

Screenshots (if relevant)

N/A

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together