[AIRFLOW-6425] Serialization: Add missing DAG parameters to Json Schema

[kaxil]

The following DAG currently fails:

Schema Validation error when DAG.is_paused_upon_creation is set

def make_simple_dag():
    """Make very simple DAG to verify serialization result."""
    dag = DAG(
        dag_id='simple_dag',
        default_args={
            "retries": 1,
            "retry_delay": timedelta(minutes=5),
            "depends_on_past": False,
        },
        start_date=datetime(2019, 8, 1),
        is_paused_upon_creation=True,
    )
    BaseOperator(task_id='simple_task', dag=dag, owner='airflow')
    CustomOperator(task_id='custom_task', dag=dag)
    return {'simple_dag': dag}

Error:

 jsonschema.exceptions.ValidationError: Additional properties are not allowed ('is_paused_upon_creation' was unexpected)

Reason:

is_paused_upon_creation is in DAG.get_serialized_fields() but not in the Schema definition.

---

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[codecov-io]

Codecov Report

Merging #7002 into master will decrease coverage by 0.27%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #7002      +/-   ##
==========================================
- Coverage   84.85%   84.57%   -0.28%     
==========================================
  Files         679      679              
  Lines       38542    38545       +3     
==========================================
- Hits        32703    32598     -105     
- Misses       5839     5947     +108

Impacted Files	Coverage Δ
airflow/models/dag.py	90.95% <ø> (ø)	⬆️
airflow/serialization/json_schema.py	84% <100%> (+2.18%)	⬆️
airflow/kubernetes/volume_mount.py	44.44% <0%> (-55.56%)	⬇️
airflow/kubernetes/volume.py	52.94% <0%> (-47.06%)	⬇️
airflow/kubernetes/pod_launcher.py	45.25% <0%> (-46.72%)	⬇️
airflow/kubernetes/refresh_config.py	50.98% <0%> (-23.53%)	⬇️
...rflow/contrib/operators/kubernetes_pod_operator.py	78.75% <0%> (-20%)	⬇️
airflow/gcp/operators/gcs.py	85.62% <0%> (-0.6%)	⬇️
airflow/jobs/backfill_job.py	91.59% <0%> (-0.29%)	⬇️
airflow/gcp/example_dags/example_gcs.py	100% <0%> (+11.42%)	⬆️

---

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