**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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with dag_maker(session=session, dag_id="test"):
        task = BaseOperator(task_id="task_1")
    dr = DagRun(dag_id="test", run_id="test", run_type=DagRunType.MANUAL)
    ti0 = TI(task=task, run_id=dr.run_id, map_index=0, state=TaskInstanceState.SUCCESS)
    ti1 = TI(task=task, run_id=dr.run_id, map_index=1, state=None)
    ti2 = TI(task=task, run_id=dr.run_id, map_index=2, state=TaskInstanceState.SUCCESS)
    session.add_all((dr, ti0, ti1, ti2))
    session.flush()
    assert dr.schedule_tis((ti1,), session=session) == 1
    session.refresh(ti0)
    session.refresh(ti1)
    session.refresh(ti2)
    assert ti0.state == TaskInstanceState.SUCCESS
    assert ti1.state == TaskInstanceState.SCHEDULED
    assert ti2.state == TaskInstanceState.SUCCESS
def test_mapped_expand_kwargs(dag_maker):
    with dag_maker():
        @task
        def task_0():
            return {"arg1": "a", "arg2": "b"}
        @task
        def task_1(args_0):
            return [args_0, {"arg1": "y"}, {"arg2": "z"}]
        args_0 = task_0()
        args_list = task_1(args_0=args_0)
        MockOperator.partial(task_id="task_2").expand_kwargs(args_list)
        MockOperator.partial(task_id="task_3").expand_kwargs(
            [{"arg1": "a", "arg2": "b"}, {"arg1": "y"}, {"arg2": "z"}],
        )
        MockOperator.partial(task_id="task_4").expand_kwargs([args_0, {"arg1": "y"}, {"arg2": "z"}])