Function create 

pub async fn create(
    pool: &PgPool,
    actor: &Actor,
    input: ChangeInput,
) -> AppResult<Change>

Creates a draft change.

Invariants

• Permission: CAD editor.
• Locks: the change counter row, held until commit, so concurrent creations get different numbers.
• Audit: change.create.
• Notifications / webhooks: none.
• Atomic: one transaction; the number is stepped in it and is not used up when it fails.