Add self-service JWT token generation to the Airflow UI (#63195)

* Add self-service JWT token generation to the Airflow UI

  Implement a full-stack feature enabling authenticated users to generate
  JWT tokens (API and CLI) directly from the Airflow web interface. This
  eliminates the need to re-authenticate or use credential-based endpoints,
  streamlining API access and airflowctl usage for all Airflow deployments.

* Xiaodong's feedback

* Fix static checks

* fix more static checks

* Jasons suggestions