Clarify default scope for issue search API

doc/api/issues.md

@@ -277,7 +277,7 @@ GET /groups/:id/issues?state=opened
 | `non_archived`      | boolean          | no         | Return issues from non archived projects. Default is true. _([Introduced](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/23785) in GitLab 12.8)_ |
 | `not`               | Hash             | no         | Return issues that do not match the parameters supplied. Accepts: `labels`, `milestone`, `author_id`, `author_username`, `assignee_id`, `assignee_username`, `my_reaction_emoji`, `search`, `in` |
 | `order_by`          | string           | no         | Return issues ordered by `created_at`, `updated_at`, `priority`, `due_date`, `relative_position`, `label_priority`, `milestone_due`, `popularity`, `weight` fields. Default is `created_at`                                                               |
-| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`. |
+| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`. Defaults to `all`. |
 | `search`            | string           | no         | Search group issues against their `title` and `description`                                                                   |
 | `sort`              | string           | no         | Return issues sorted in `asc` or `desc` order. Default is `desc`                                                              |
 | `state`             | string           | no         | Return all issues or just those that are `opened` or `closed`                                                                 |
@@ -476,7 +476,7 @@ GET /projects/:id/issues?state=opened
 | `my_reaction_emoji` | string           | no         | Return issues reacted by the authenticated user by the given `emoji`. `None` returns issues not given a reaction. `Any` returns issues given at least one reaction. |
 | `not`               | Hash             | no         | Return issues that do not match the parameters supplied. Accepts: `labels`, `milestone`, `author_id`, `author_username`, `assignee_id`, `assignee_username`, `my_reaction_emoji`, `search`, `in` |
 | `order_by`          | string           | no         | Return issues ordered by `created_at`, `updated_at`, `priority`, `due_date`, `relative_position`, `label_priority`, `milestone_due`, `popularity`, `weight` fields. Default is `created_at`                                                               |
-| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`. |
+| `scope`             | string           | no         | Return issues for the given scope: `created_by_me`, `assigned_to_me` or `all`. Defaults to `all`. |
 | `search`            | string           | no         | Search project issues against their `title` and `description`                                                                 |
 | `sort`              | string           | no         | Return issues sorted in `asc` or `desc` order. Default is `desc`                                                              |
 | `state`             | string           | no         | Return all issues or just those that are `opened` or `closed`                                                                 |