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)

The issue names no Airflow files, tests, or entry points; start by reviewing the linked airflow-dag-operator project and Airflow's existing Kubernetes and git-sync integration. Define the CRD, synchronization behavior, and Airflow deployment changes needed to sync DAGs and other files to each pod, with tests and documentation demonstrating the completed workflow.

Written by the indexing model from the issue text.