**Description**

We need to have the endpoint in Airflow V1 to retrieve details of existing DAG, e.g. `GET /dags/{dag_id}/details `

**Use case / motivation**

We want to be able to retrieve/discover the parameters that a DAG accepts. We can see that you pass parameters when you execute a dag via the conf object. We can also see that you explicitly declare parameters that a DAG accepts via the params argument when creating the DAG.
However, we can't see anywhere via either the REST API or CLI that allows you to retrieve this information from a DAG (note that we are not saying a DAG run).
It doesn't even look like version 2 API supports this although the OpenAPI spec mentions a dags/{dag_id}/details endpoint but this is not documented. We found the related GitHub issue for this new endpoint and it is done but looks like documentation isn't yet updated.
Please can you:

1. Provide the response for the v2 details endpoint
2. Advise when v2 documentation will be updated with the details endpoint.
3. Advise if there is a workaround for us doing this on v1.1

**Related Issues**

#8138 

airflow/api_connexion/schemas/dag_schema.py
"""DAG details"""
    timezone = TimezoneField(dump_only=True)
    catchup = fields.Boolean(dump_only=True)
    orientation = fields.String(dump_only=True)
    concurrency = fields.Integer(dump_only=True)
    start_date = fields.DateTime(dump_only=True)
    dag_run_timeout = fields.Nested(TimeDeltaSchema, dump_only=True, attribute="dagrun_timeout")
    doc_md = fields.String(dump_only=True)
    default_view = fields.String(dump_only=True)
class DAGCollection(NamedTuple):
    """List of DAGs with metadata"""
    dags: List[DagModel]
    total_entries: int
class DAGCollectionSchema(Schema):
    """DAG Collection schema"""
    dags = fields.List(fields.Nested(DAGSchema))
    total_entries = fields.Int()
dags_collection_schema = DAGCollectionSchema()
dag_schema = DAGSchema()
dag_detail_schema = DAGDetailSchema()