Add doc strings for create and update group API

doc/api/groups.md

@@ -492,6 +492,7 @@ Parameters:
 | `auto_devops_enabled`                | boolean | no       | Default to Auto DevOps pipeline for all projects within this group. |
 | `subgroup_creation_level`            | string  | no       | Allowed to create subgroups. Can be `owner` (Owners), or `maintainer` (Maintainers). |
 | `emails_disabled`                    | boolean | no       | Disable email notifications |
+| `avatar`                             | mixed   | no       | Image file for avatar of the group |
 | `mentions_disabled`                  | boolean | no       | Disable the capability of a group from getting mentioned |
 | `lfs_enabled`                        | boolean | no       | Enable/disable Large File Storage (LFS) for the projects in this group. |
 | `request_access_enabled`             | boolean | no       | Allow users to request member access. |
@@ -553,6 +554,7 @@ PUT /groups/:id
 | `auto_devops_enabled`                | boolean | no       | Default to Auto DevOps pipeline for all projects within this group. |
 | `subgroup_creation_level`            | string  | no       | Allowed to create subgroups. Can be `owner` (Owners), or `maintainer` (Maintainers). |
 | `emails_disabled`                    | boolean | no       | Disable email notifications |
+| `avatar`                             | mixed   | no       | Image file for avatar of the group |
 | `mentions_disabled`                  | boolean | no       | Disable the capability of a group from getting mentioned |
 | `lfs_enabled` (optional)             | boolean | no       | Enable/disable Large File Storage (LFS) for the projects in this group. |
 | `request_access_enabled`             | boolean | no       | Allow users to request member access. |

spec/requests/api/groups_spec.rb

@@ -1003,7 +1003,7 @@ describe API::Groups do
 
       it "uploads avatar for a group" do
         group = attributes_for_group_api request_access_enabled: false
-        group.merge!(avatar: fixture_file_upload('spec/fixtures/banana_sample.gif', 'image/gif'))
+        group[:avatar] = fixture_file_upload('spec/fixtures/banana_sample.gif', 'image/gif')
 
         post api("/groups", user3), params: group