**Description**


It would be great if the metrics we publish in Airflow change to include TAGs for "variable" parts of those (such as dag_id, task_id, pool name) rather than being part of the metrics.

See here: https://airflow.apache.org/docs/1.10.12/metrics.html, https://airflow.readthedocs.io/en/latest/logging-monitoring/metrics.html  - those variable parts should be tags.

We might consider to change those metrics by default in 2.0 and possibly introduce a backport in 1.10.13 to allow people to migrate.


**Use case / motivation**

Having the variable parts of the metrics makes it really difficult to aggregate the metrics. Seems that statsd python library does not support tags, but there are possible solutions by installing extensions:

https://stackoverflow.com/questions/49852654/sending-statsd-metrics-with-tags-from-python-client

**Related Issues**

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)
        runs = DagRun.next_dagruns_to_examine(state, session).all()
        assert runs == [dr]
        orm_dag.is_paused = True
        session.flush()
        runs = DagRun.next_dagruns_to_examine(state, session).all()
        assert runs == []
    @mock.patch.object(Stats, "timing")
    def test_no_scheduling_delay_for_nonscheduled_runs(self, stats_mock, session):
        """
        Tests that dag scheduling delay stat is not called if the dagrun is not a scheduled run.
        This case is manual run. Simple test for coherence check.
        """
        dag = DAG(dag_id="test_dagrun_stats", start_date=DEFAULT_DATE)
        dag_task = EmptyOperator(task_id="dummy", dag=dag)
        initial_task_states = {
            dag_task.task_id: TaskInstanceState.SUCCESS,
        }
        dag_run = self.create_dag_run(dag=dag, task_states=initial_task_states, session=session)
        dag_run.update_state()
        assert call(f"dagrun.{dag.dag_id}.first_task_scheduling_delay") not in stats_mock.mock_calls
    @pytest.mark.parametrize(
        "schedule_interval, expected",
        [
            ("*/5 * * * *", True),
            (None, False),
            ("@once", False),
        ],
    )
    def test_emit_scheduling_delay(self, session, schedule_interval, expected):