AIP-84 Migrate backfill API to fast api

[dstandish]

Related to #42370

That is all.

[pierrejeambrun]

Looking great overall.

A few minor suggestions

[pierrejeambrun]

Looking good, thanks Daniel

[potiuk]

Ah...

FAILED providers/tests/fab/auth_manager/api_endpoints/test_backfill_endpoint.py::TestListBackfills::test_should_respond_200_with_granular_dag_access - assert 404 == 200
 +  where 404 = <WrapperTestResponse streamed [404 NOT FOUND]>.status_code
FAILED providers/tests/fab/auth_manager/api_endpoints/test_backfill_endpoint.py::TestGetBackfill::test_should_respond_200_with_granular_dag_access - assert 404 == 200
 +  where 404 = <WrapperTestResponse streamed [404 NOT FOUND]>.status_code
FAILED providers/tests/fab/auth_manager/api_endpoints/test_backfill_endpoint.py::TestCreateBackfill::test_create_backfill - assert 404 == 200
 +  where 404 = <WrapperTestResponse streamed [404 NOT FOUND]>.status_code
FAILED providers/tests/fab/auth_manager/api_endpoints/test_backfill_endpoint.py::TestPauseBackfill::test_should_respond_200_with_granular_dag_access - assert 404 == 200
 +  where 404 = <WrapperTestResponse streamed [404 NOT FOUND]>.status_code
FAILED providers/tests/fab/auth_manager/api_endpoints/test_backfill_endpoint.py::TestCancelBackfill::test_should_respond_200_with_granular_dag_access - assert 404 == 200
 +  where 404 = <WrapperTestResponse streamed [404 NOT FOUND]>.status_code

Will faili now in main - see https://github.com/apache/airflow/actions/runs/11669732900/job/32492756690?pr=43556#step:7:4733

I guess those tests should never be in FAB in the first place ? Maybe we should move them to API @dstandish @pierrejeambrun

[potiuk]

It's nice to see with all those changes how sometimes mixed things were :D

[pierrejeambrun]

Yep, we missed that FAB provider tests were relying on these legacy endpoints. Indeed those should not be there in the first place, Daniel opened quickly a PR to fix it, sorry for the disruption.