Integrate DAG editor in Airflow

[Maleware]

Current Situation

We offer the customer to inject DAGs into airflow in two ways:

1. Customers can mount a configMap into the Airflow pod and store the DAGs there.
2. Customers can use GitSync to host DAGs in an git repository.

Both ways need a way to interact either with kubernetes itself or with git.

Proposed Situation

Customers can log into Airflow and edit DAGs in the Airflow UI.

To archive this, we'd need to include an editor in airflow dockerimage and make it configurable through the operators CRD. I'd propose https://github.com/andreax79/airflow-code-editor as an candidate.

Advantage

Now where #573 is merged, we offer deeply integrated Open Policy Agent support, which would lead to the advantage to offer role based editor access to data engineers or product owners. There wouldn't be a need to have knowledge of kuberentes or git to modify, develop and deploy DAGs. In my opinion this would increase usability and accessibility of Airflow and could empower the customer.

Additionally, it would make the development process of DAGs much easier as we would move from develop -> deploy -> test to develop -> test.

Evaluation

I expect this to be a rather large feature. We'd need to think about roles and how to configure those for editor access without OPA too. We need to be able to integrate with GitSync and implement access, provisioning and usage of PVCs to store DAGs written in the Airflow UI. Role based access may also apply to files stored in PVCs. We introduce at least another dependency we might need to maintain.