**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 to check that a DAG returns its active runs
        """
        now = timezone.utcnow()
        six_hours_ago_to_the_hour = (now - datetime.timedelta(hours=6)).replace(
            minute=0, second=0, microsecond=0
        )
        start_date = six_hours_ago_to_the_hour
        dag_name1 = "get_active_runs_test"
        default_args = {"depends_on_past": False, "start_date": start_date}
        with dag_maker(dag_name1, schedule="* * * * *", max_active_runs=1, default_args=default_args) as dag1:
            run_this_1 = EmptyOperator(task_id="run_this_1")
            run_this_2 = EmptyOperator(task_id="run_this_2")
            run_this_2.set_upstream(run_this_1)
            run_this_3 = EmptyOperator(task_id="run_this_3")
            run_this_3.set_upstream(run_this_2)
        dr = dag_maker.create_dagrun()
        
        assert dr is not None
        execution_date = dr.execution_date
        running_dates = dag1.get_active_runs()
        try:
            running_date = running_dates[0]
        except Exception:
            running_date = "Except"
        assert execution_date == running_date, "Running Date must match Execution Date"
    def test_list_py_file_paths(self):