**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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"""
        Test that _start_dagrun:
        - moves runs to RUNNING State
        - emit the right DagRun metrics
        """
        with dag_maker(dag_id="test_start_dag_runs") as dag:
            EmptyOperator(
                task_id="dummy",
            )
        dag_model = dag_maker.dag_model
        self.scheduler_job = SchedulerJob(executor=self.null_exec)
        self.scheduler_job.processor_agent = mock.MagicMock()
        with create_session() as session:
            self.scheduler_job._create_dag_runs([dag_model], session)
            self.scheduler_job._start_queued_dagruns(session)
        dr = session.query(DagRun).filter(DagRun.dag_id == dag.dag_id).first()
        
        assert dr.state == State.RUNNING
        stats_timing.assert_called_once_with(
            "dagrun.schedule_delay.test_start_dag_runs", datetime.timedelta(seconds=9)
        )
        assert dag.get_last_dagrun().creating_job_id == self.scheduler_job.id
    def test_extra_operator_links_not_loaded_in_scheduler_loop(self, dag_maker):