**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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from airflow.models.pool import Pool
        pools = Pool.slots_stats(session=session)
        for pool_name, slot_stats in pools.items():
            Stats.gauge(f"pool.open_slots.{pool_name}", slot_stats["open"])
            Stats.gauge(f"pool.queued_slots.{pool_name}", slot_stats["queued"])
            Stats.gauge(f"pool.running_slots.{pool_name}", slot_stats["running"])
    @provide_session
    def heartbeat_callback(self, session: Session = NEW_SESSION) -> None:
        Stats.incr("scheduler_heartbeat", 1, 1)
    @provide_session
    def adopt_or_reset_orphaned_tasks(self, session: Session = NEW_SESSION) -> int:
        """
        Reset any TaskInstance still in QUEUED or SCHEDULED states that were
        enqueued by a SchedulerJob that is no longer running.
        :return: the number of TIs reset
        """
        self.log.info("Resetting orphaned tasks for active dag runs")
        timeout = conf.getint("scheduler", "scheduler_health_check_threshold")
        for attempt in run_with_db_retries(logger=self.log):
            with attempt:
                self.log.debug(
                    "Running SchedulerJob.adopt_or_reset_orphaned_tasks with retries. Try %d of %d",
                    attempt.retry_state.attempt_number,
                    MAX_DB_RETRIES,
                )
                self.log.debug("Calling SchedulerJob.adopt_or_reset_orphaned_tasks method")