**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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with conf_vars(configs):
            self.scheduler_job = SchedulerJob(None, heartrate=10, state=State.RUNNING)
            assert self.scheduler_job.is_alive()
            self.scheduler_job.latest_heartbeat = timezone.utcnow() - datetime.timedelta(seconds=20)
            assert self.scheduler_job.is_alive()
            self.scheduler_job.latest_heartbeat = timezone.utcnow() - datetime.timedelta(seconds=31)
            assert not self.scheduler_job.is_alive()
            
            
            self.scheduler_job.latest_heartbeat = timezone.utcnow() - datetime.timedelta(days=1)
            assert not self.scheduler_job.is_alive()
            self.scheduler_job.state = State.SUCCESS
            self.scheduler_job.latest_heartbeat = timezone.utcnow() - datetime.timedelta(seconds=10)
            assert (
                not self.scheduler_job.is_alive()
            ), "Completed jobs even with recent heartbeat should not be alive"
    def run_single_scheduler_loop_with_no_dags(self, dags_folder):
        """
        Utility function that runs a single scheduler loop without actually
        changing/scheduling any dags. This is useful to simulate the other side effects of
        running a scheduler loop, e.g. to see what parse errors there are in the
        dags_folder.
        :param dags_folder: the directory to traverse
        """
        self.scheduler_job = SchedulerJob(
            executor=self.null_exec, num_times_parse_dags=1, subdir=os.path.join(dags_folder)
        )
        self.scheduler_job.heartrate = 0
        self.scheduler_job.run()
    def test_no_orphan_process_will_be_left(self):