Update dag endpoint tests to include dags with deadlines

[rawwar]

Description

Need to update tests to create DAGs with deadlines as below:

with dag_maker(
            DAG1_ID,
            dag_display_name=DAG1_DISPLAY_NAME,
            schedule=None,
            start_date=DAG1_START_DATE,
            doc_md="details",
            default_args={
                "depends_on_past": False,
                "retries": 1,
                "retry_delay": timedelta(minutes=5),
            },
            deadline=[DeadlineAlert(
                reference=DeadlineReference.DAGRUN_LOGICAL_DATE,
                interval=timedelta(hours=1),
                callback="dummy.callback",
            )],
            params={"foo": 1},
            tags=["example"],
        ):
            EmptyOperator(task_id=TASK_ID)

Use case/motivation

No response

Related issues

related to #50574

Are you willing to submit a PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[rawwar]

Currently,

in DAG class, deadline is defined as

deadline: DeadlineAlert | None = attrs.field(
        default=None,
        validator=attrs.validators.optional(attrs.validators.instance_of(DeadlineAlert)),
    )

This needs to change, in order to allow multiple DeadlineAlert's . And that's a blocker

[ambika-garg]

Hey @rawwar, I'm willing to take up this task, can you please assign it to me?
I believe I’ll be able to start working on it once PR #50957 is merged.

[ej-sanmartin]

Seems self contained and I'm interested in working on this. @ambika-garg are you still interested in taking this issue on?