docs: update created_at docs for creating issues via API

See also #19863.

Fixes #18458.

doc/api/issues.md

@@ -323,7 +323,7 @@ POST /projects/:id/issues
 | `assignee_id`   | integer | no  | The ID of a user to assign issue |
 | `milestone_id`  | integer | no  | The ID of a milestone to assign issue |
 | `labels`        | string  | no  | Comma-separated label names for an issue  |
-| `created_at`    | string  | no  | Date time string, ISO 8601 formatted, e.g. `2016-03-11T03:45:40Z` |
+| `created_at`    | string  | no  | Date time string, ISO 8601 formatted, e.g. `2016-03-11T03:45:40Z` (requires admin or project owner rights) |
 | `due_date`      | string  | no   | Date time string in the format YEAR-MONTH-DAY, e.g. `2016-03-11` |
 
 ```bash
@@ -384,7 +384,7 @@ PUT /projects/:id/issues/:issue_id
 | `milestone_id`  | integer | no  | The ID of a milestone to assign the issue to |
 | `labels`        | string  | no  | Comma-separated label names for an issue  |
 | `state_event`   | string  | no  | The state event of an issue. Set `close` to close the issue and `reopen` to reopen it |
-| `updated_at`    | string  | no  | Date time string, ISO 8601 formatted, e.g. `2016-03-11T03:45:40Z` |
+| `updated_at`    | string  | no  | Date time string, ISO 8601 formatted, e.g. `2016-03-11T03:45:40Z` (requires admin or project owner rights) |
 | `due_date`      | string  | no   | Date time string in the format YEAR-MONTH-DAY, e.g. `2016-03-11` |
 
 ```bash