The GitLab project ID was still hardcoded to my playground project on
GitLab.com.
This commit instead reads from the predefined GitLab CI/CD variable for
the projects ID (`CI_PROJECT_ID`).
Makes navigating to the PR way easier when looking at the logs.
This requires a new `Forge.PullRequestURL()` method that needs to be
implemented for all forges.
- PR Description
- Read prefix+suffix from PR description and put into changelog
- Keep those overrides on PR description changes
- Add pending level to new PRs