AIP-72: Allow retrieving Connection from Task Context

[kaxil]

part of #44481

• Added a minimal Connection user-facing object in Task SDK definition for use in the DAG file
• Added logic to get Connections in the context. Fixed some bugs in the way related to Connection parsing/serializing!

Now, we have following Connection related objects:

• ConnectionResponse is auto-generated and tightly coupled with the API schema.
• ConnectionResult is runtime-specific and meant for internal communication between Supervisor & Task Runner.
• Connection class here is where the public-facing, user-relevant aspects are exposed, hiding internal details.

Next up:

• Same for XCom & Variable
• Implementation of BaseHook.get_conn

Tested it with a DAG:

DAG:

from __future__ import annotations

from airflow.models.baseoperator import BaseOperator
from airflow.models.dag import dag


class CustomOperator(BaseOperator):
    def execute(self, context):
        import os
        os.environ["AIRFLOW_CONN_AIRFLOW_DB"] = "sqlite:///home/airflow/airflow.db"
        task_id = context["task_instance"].task_id
        print(f"Hello World {task_id}!")
        print(context)
        print(context["conn"].airflow_db)
        assert context["conn"].airflow_db.conn_id == "airflow_db"


@dag()
def super_basic_run():
    CustomOperator(task_id="hello")


super_basic_run()

For case where a connection is not found

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[ashb]

My comments have been addressed

[amoghrajesh]

Some comments lying open, rest LGTM