Description

We need a common mechanism for deserialization and serialization of Python objects.

PR with this change should define all schemas with Python objects (DAG. BaseOperator) in accordance with OpenAPI specification

More information about REST API:
#8107

Use case / motivation

This will make writing new endpoints much easier. We will also have one place defining the structure, which will facilitate backward compatibility.

Related Issues

This task is related to
#8110
#8114
#8115
It was divided so that we could do the work with smaller pieces.