**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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"""
        Set the given task instances in to the scheduled state.
        Each element of ``schedulable_tis`` should have it's ``task`` attribute already set.
        Any EmptyOperator without callbacks or outlets is instead set straight to the success state.
        All the TIs should belong to this DagRun, but this code is in the hot-path, this is not checked -- it
        is the caller's responsibility to call this function only with TIs from a single dag run.
        """
        
        
        dummy_ti_ids = []
        schedulable_ti_ids = []
        for ti in schedulable_tis:
            if (
                ti.task.inherits_from_empty_operator
                and not ti.task.on_execute_callback
                and not ti.task.on_success_callback
                and not ti.task.outlets
            ):
                dummy_ti_ids.append(ti.task_id)
            else:
                schedulable_ti_ids.append((ti.task_id, ti.map_index))
        count = 0
        if schedulable_ti_ids:
            count += (