**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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dr.dag = serialized_dag
    
    ti = dr.get_task_instance(task_id="task_1")
    task1 = dag.get_task("task_1")
    ti.refresh_from_task(task1)
    ti.run()
    task2 = dag.get_task("task_2")
    for ti in dr.get_task_instances():
        if ti.map_index < 0:
            ti.task = task1
        else:
            ti.task = task2
        session.merge(ti)
    session.flush()
    with caplog.at_level(logging.DEBUG):
        
        dr.verify_integrity()
        tis = dr.get_task_instances()
        indices = [(ti.map_index, ti.state) for ti in tis if ti.map_index >= 0]
        assert sorted(indices) == [
            (0, TaskInstanceState.REMOVED),
            (1, TaskInstanceState.REMOVED),
            (2, TaskInstanceState.REMOVED),
        ]
        assert (
            f"Removing task '{ti1}' as the map_index is longer than the resolved mapping list (0)"
            in caplog.text
        )
@pytest.mark.need_serialized_dag
def test_mapped_mixed_literal_not_expanded_at_create(dag_maker, session):