Dot-Project: backfill `maintainers.csv` from `.project/maintainers.yml` when applicable

For the Orgs that has adopted the `.project`, we should backfill the `maintainers.csv` file untill the adoption of `.project` is complete across all CNCF Orgs.

Once the org has adopted the `.project`, it replaces the csv file, however, during the adoption process of `.project`, we need to maintain resouces access in a unifed place.