**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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num_finished_events = self._process_executor_events(session=session)
                if self.processor_agent:
                    self.processor_agent.heartbeat()
                
                self.heartbeat(only_if_necessary=True)
                
                next_event = timers.run(blocking=False)
                self.log.debug("Next timed event is in %f", next_event)
            self.log.debug("Ran scheduling loop in %.2f seconds", timer.duration)
            if not is_unit_test and not num_queued_tis and not num_finished_events:
                
                
                
                time.sleep(min(self._scheduler_idle_sleep_time, next_event if next_event else 0))
            if loop_count >= self.num_runs > 0:
                self.log.info(
                    "Exiting scheduler loop as requested number of runs (%d - got to %d) has been reached",
                    self.num_runs,
                    loop_count,
                )
                break
            if self.processor_agent and self.processor_agent.done:
                self.log.info(
                    "Exiting scheduler loop as requested DAG parse count (%d) has been reached after %d"
                    " scheduler loops",
                    self.num_times_parse_dags,
                    loop_count,
                )
                break
    def _do_scheduling(self, session: Session) -> int: