Add GitLab REST API client and IssueCreator for drupal.org GitLab projects
### Problem/Motivation Implement a GitLab backend for the issue creation system parallel to the existing drupal.org support. Add a thin HTTP client with GET/POST/getRaw methods, GitLab IssueCreator with marker-based issue discovery and creation, routing logic to delegate GitLab-backed projects to the new backend, configuration keys for PAT and project path, and per-project backend detection via HEAD redirects. Cover the full round-trip with 24+ unit tests including marker-based adoption and MR interdiff change detection. ### Work items - Commit(s): [7905fd8d9d](https://git.drupalcode.org/project/project_analysis/-/commit/7905fd8d9d8d), [9b03686abc](https://git.drupalcode.org/project/project_analysis/-/commit/9b03686abcb6), [f8c8fd78e8](https://git.drupalcode.org/project/project_analysis/-/commit/f8c8fd78e801), [dbf9a49ea6](https://git.drupalcode.org/project/project_analysis/-/commit/dbf9a49ea68a), [f8d7510eb9](https://git.drupalcode.org/project/project_analysis/-/commit/f8d7510eb9a8) ### Credit - Implemented by: @bbrala --- *Filed retroactively as part of the Drupal 12 rector coverage effort. Closed as fixed; credit to be applied to the contributors listed above.* *AI was used extensively to build this work and to file this issue. See [Dries Buytaert: AI-generated Rector rules for Drupal](https://dri.es/ai-generated-rector-rules-for-drupal) and [Björn Brala: Drupal Rector rules are config, not code. Mostly.](https://www.linkedin.com/pulse/drupal-rector-rules-config-code-mostly-bj%C3%B6rn-brala-vfpwe/).*
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