GitHub Importer - Migrate issue 'un/labeled' events

Problem to solve

When migrating projects from GitHub to GitLab, the issues are imported including any comments. However, any history/events are not migrated over. This means that, after the migration, the users would not be able to see who added/removed labels, milestones, assignees, etc.

For some users this is a dealbreaker that would prevent them from migrating to GitLab.

Proposed solution

During project import from GitHub, for each imported issue, check if any events of type labeled or unlabeled exist for that issue and create corresponding events in GitLab.

Screenshots

These images illustrate the expected result in GitLab for each event in GitHub:

GitHub	➡️	GitLab
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👣 This issue

This issue is to migrate the following events:

• labeled
  • This event is triggered when a label is assigned to an issue.
  • GitHub API doc: https://docs.github.com/en/developers/webhooks-and-events/events/issue-event-types#labeled
• unlabeled
  • This event is triggered when a label is unassigned from an issue.
  • GitHub API doc: https://docs.github.com/en/developers/webhooks-and-events/events/issue-event-types#unlabeled

Iteration plan

1. 👣 GitHub Importer - Migrate issue 'closed/reopene... (#354234 - closed)
2. 👣 GitHub Importer - Migrate issue 'un/labeled' ev... (#354235 - closed) - THIS ISSUE
3. 👣 GitHub Importer - Migrate issue 'de/milestoned'... (#354236 - closed)
4. 👣 GitHub Importer - Migrate issue 'cross-referenc... (#354238 - closed)
5. 👣 GitHub Importer - Migrate issue 'un/assigned' e... (#354237 - closed)
6. 👣 GitHub Importer - Migrate issue 'renamed' events (#354239 - closed)

Technical details

Per GitHub API documentation:

• we can use GET /repos/{owner}/{repo}/issues/{issue_number}/events to get a list of events for an issue

Documentation

• 📖 User doc: https://docs.gitlab.com/ee/user/project/import/github.html
• 📖 Developer doc: https://docs.gitlab.com/ee/development/github_importer.html