Add a CRD-sync on k8s

### Description Airflow use `git-sync` to pull DAGs from git repository, I'm thinking about doing it in a more cloud native way. So I thought of using k8s `custom resource definition` to do this. We can migrate DAG, files and other contents to `custom resource definition`. Based on the operator by a container, we can instantly synchronize them to each pod of Airflow. ### Use case/motivation I have created a project on GitHub to implement this idea https://github.com/cdmikechen/airflow-dag-operator. It will start a synchronization service with [Quarkus Operator](https://github.com/quarkiverse/quarkus-operator-sdk) on each airflow pod to synchronize the DAG/files into the DAG folder. ### Related issues _No response_ ### Are you willing to submit a PR? - [X] Yes I am willing to submit a PR! ### Code of Conduct - [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)