API documentation, changelog and additional tests for YouTrack integration service

changelogs/unreleased/add-youtrack-integration.yml

+---
+title: Add YouTrack integration service
+merge_request: 25361
+author: Yauhen Kotau @bessorion
+type: added

doc/api/services.md

@@ -1101,3 +1101,39 @@ GET /projects/:id/services/mock-ci
 ```
 
 [11435]: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11435
+
+## YouTrack
+
+YouTrack issue tracker
+
+### Create/Edit YouTrack service
+
+Set YouTrack service for a project.
+
+```
+PUT /projects/:id/services/youtrack
+```
+
+Parameters:
+
+| Parameter | Type | Required | Description |
+| --------- | ---- | -------- | ----------- |
+| `issues_url` | string | true | Issue url |
+| `project_url` | string | true | Project url |
+| `description` | string | false | Description |
+
+### Delete YouTrack Service
+
+Delete YouTrack service for a project.
+
+```
+DELETE /projects/:id/services/youtrack
+```
+
+### Get YouTrack Service Settings
+
+Get YouTrack service settings for a project.
+
+```
+GET /projects/:id/services/youtrack
+```

spec/models/project_spec.rb

@@ -50,6 +50,7 @@ describe Project do
     it { is_expected.to have_one(:teamcity_service) }
     it { is_expected.to have_one(:jira_service) }
     it { is_expected.to have_one(:redmine_service) }
+    it { is_expected.to have_one(:youtrack_service) }
     it { is_expected.to have_one(:custom_issue_tracker_service) }
     it { is_expected.to have_one(:bugzilla_service) }
     it { is_expected.to have_one(:gitlab_issue_tracker_service) }