**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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return (
                    bool(self.tis)
                    and all(not t.task.depends_on_past for t in self.tis)
                    and all(t.task.max_active_tis_per_dag is None for t in self.tis)
                    and all(t.state != TaskInstanceState.DEFERRED for t in self.tis)
                )
            def recalculate(self) -> _UnfinishedStates:
                return self._replace(tis=[t for t in self.tis if t.state in State.unfinished])
        start_dttm = timezone.utcnow()
        self.last_scheduling_decision = start_dttm
        with Stats.timer(f"dagrun.dependency-check.{self.dag_id}"):
            dag = self.get_dag()
            info = self.task_instance_scheduling_decisions(session)
            tis = info.tis
            schedulable_tis = info.schedulable_tis
            changed_tis = info.changed_tis
            finished_tis = info.finished_tis
            unfinished = _UnfinishedStates.calculate(info.unfinished_tis)
            if unfinished.should_schedule:
                are_runnable_tasks = schedulable_tis or changed_tis
                
                if not are_runnable_tasks:
                    are_runnable_tasks, changed_by_upstream = self._are_premature_tis(
                        unfinished.tis, finished_tis, session
                    )
                    if changed_by_upstream:  
                        unfinished = unfinished.recalculate()
        leaf_task_ids = {t.task_id for t in dag.leaves}