**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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scheduler.processor_agent = mock.MagicMock()
        def _create_dagruns(dag: DAG):
            next_info = dag.next_dagrun_info(None)
            assert next_info is not None
            for _ in range(30):
                yield dag.create_dagrun(
                    run_type=DagRunType.SCHEDULED,
                    execution_date=next_info.logical_date,
                    data_interval=next_info.data_interval,
                    state=DagRunState.RUNNING,
                )
                next_info = dag.next_dagrun_info(next_info.data_interval)
                if next_info is None:
                    break
        
        
        
        for dr in _create_dagruns(dag_d1):
            scheduler._schedule_dag_run(dr, session)
        for dr in _create_dagruns(dag_d2):
            scheduler._schedule_dag_run(dr, session)
        scheduler._executable_task_instances_to_queued(max_tis=2, session=session)
        task_instances_list2 = scheduler._executable_task_instances_to_queued(max_tis=2, session=session)
        
        assert len(task_instances_list2) > 0
        assert all(
            task_instance.pool != "test_scheduler_keeps_scheduling_pool_full_p1"
            for task_instance in task_instances_list2
        )
    def test_scheduler_verify_priority_and_slots(self, dag_maker):