Merge branch 'docs-improve-issues-api-description' into 'master'

Docs: improve issues API description

See merge request gitlab-org/gitlab!41215

doc/api/issues.md

@@ -2080,8 +2080,8 @@ GET /projects/:id/issues/:issue_iid/closed_by
 ```
 
 | Attribute   | Type           | Required | Description                        |
-| ---------   | ----    | -------- | -----------                          |
-| `id`        | integer | yes      | The ID of a project                  |
+| ----------- | ---------------| -------- | ---------------------------------- |
+| `id`        | integer/string | yes      | The ID or [URL-encoded path of the project](./README.md#namespaced-path-encoding) owned by the authenticated user |
 | `issue_iid` | integer        | yes      | The internal ID of a project issue |
 
 ```shell