Add migrate from OneDev (#16356)

* Use context to simplify logic.

* Added migration from OneDev.
This PR adds [OneDev](https://code.onedev.io/) as migration source.

Supported:
- [x] Milestones
- [x] Issues
- [x] Pull Requests
- [x] Comments
- [x] Reviews
- [x] Labels

options/locale/locale_en-US.ini

@@ -904,6 +904,7 @@ migrate.git.description = Migrating or Mirroring git data from Git services
 migrate.gitlab.description = Migrating data from GitLab.com or Self-Hosted gitlab server.
 migrate.gitea.description = Migrating data from Gitea.com or Self-Hosted Gitea server.
 migrate.gogs.description = Migrating data from notabug.org or other Self-Hosted Gogs server.
+migrate.onedev.description = Migrating data from code.onedev.io or Self-Hosted OneDev server.
 migrate.migrating_git = Migrating Git Data
 migrate.migrating_topics = Migrating Topics
 migrate.migrating_milestones = Migrating Milestones