AIP-38 | Add API Endpoint to serve connection types and extra form meta data

[jscheffl]

Body

To be able to implement #47496 and #47497 the connection types and extra form elements meta data needs to be served by an additional API endpoint.

Note: The extra form parameters should be served in the same structure and format like the DAG params such that the form elements of FlexibleForm can be re-used in the UI.

Assumption is that the needed connection types are serialized in a DB table. (No dependency to providers manager should be added to API server)

Committer

• I acknowledge that I am a maintainer/committer of the Apache Airflow project.