Integrate ipynb2md to Gitlab

ipynb2md (https://gitlab.com/gitlab-org/incubation-engineering/mlops/ipynb2md) creates a markdown version of Jupyter The flow we expect is:

1. User commits a change to one or more notebooks
2. Before creating the diff, we transform the old version and new version of each notebook to markdown using ipynb2md
3. Diff are generated with the converted files
4. A diff_batch.json is generated using a regular viewer for text

Tasks

• Add a Test covering current .ipynb diff : https://gitlab.com/gitlab-org/gitaly/blob/f8946a7c774dc0a2cffec5ec3456024fca6d808c/internal/gitaly/service/diff/commit_test.go#L18-18 (should pass)
• Add test suite covering expected new .ipynb diff (should fail)
• Add an additional parameter to diff endpoint to enable ipynb diff using ipynb2md
• Implement the conversion