Add TODOs in providers code for Subdag code removal

Follow-up of apache#41390 (comment)

Author: kaxil

airflow/providers/cncf/kubernetes/operators/pod.py

@@ -495,6 +495,7 @@ def _get_ti_pod_labels(context: Context | None = None, include_try_number: bool
         if include_try_number:
             labels.update(try_number=ti.try_number)
         # In the case of sub dags this is just useful
+        # TODO: Remove this when the minimum version of Airflow is bumped to 3.0
         if getattr(context["dag"], "parent_dag", False):
             labels["parent_dag_id"] = context["dag"].parent_dag.dag_id  # type: ignore[attr-defined]
 

airflow/providers/cncf/kubernetes/operators/spark_kubernetes.py

@@ -202,6 +202,7 @@ def create_labels_for_pod(context: dict | None = None, include_try_number: bool
             labels.update(try_number=ti.try_number)
 
         # In the case of sub dags this is just useful
+        # TODO: Remove this when the minimum version of Airflow is bumped to 3.0
         if getattr(context["dag"], "is_subdag", False):
             labels["parent_dag_id"] = context["dag"].parent_dag.dag_id
         # Ensure that label is valid for Kube,

airflow/providers/fab/auth_manager/security_manager/override.py

@@ -1003,6 +1003,7 @@ def create_dag_specific_permissions(self) -> None:
         dags = dagbag.dags.values()
 
         for dag in dags:
+            # TODO: Remove this when the minimum version of Airflow is bumped to 3.0
             root_dag_id = (getattr(dag, "parent_dag", None) or dag).dag_id
             for resource_name, resource_values in self.RESOURCE_DETAILS_MAP.items():
                 dag_resource_name = self._resource_name(root_dag_id, resource_name)
@@ -2733,6 +2734,7 @@ def filter_roles_by_perm_with_action(self, action_name: str, role_ids: list[int]
         ).all()
 
     def _get_root_dag_id(self, dag_id: str) -> str:
+        # TODO: The "root_dag_id" check can be remove when the minimum version of Airflow is bumped to 3.0
         if "." in dag_id and hasattr(DagModel, "root_dag_id"):
             dm = self.appbuilder.get_session.execute(
                 select(DagModel.dag_id, DagModel.root_dag_id).where(DagModel.dag_id == dag_id)