**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**

<!-- Is there currently another issue associated with this? -->

assert tis[0].state == State.SCHEDULED
            assert tis[1].state == State.SCHEDULED
    def test_scheduler_job_add_new_task(self, dag_maker):
        """
        Test if a task instance will be added if the dag is updated
        """
        with dag_maker(dag_id="test_scheduler_add_new_task") as dag:
            BashOperator(task_id="dummy", bash_command="echo test")
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.dagbag = dag_maker.dagbag
        session = settings.Session()
        orm_dag = dag_maker.dag_model
        assert orm_dag is not None
        if self.scheduler_job.processor_agent:
            self.scheduler_job.processor_agent.end()
        self.scheduler_job = SchedulerJob(subdir=os.devnull)
        self.scheduler_job.processor_agent = mock.MagicMock()
        dag = self.scheduler_job.dagbag.get_dag("test_scheduler_add_new_task", session=session)
        self.scheduler_job._create_dag_runs([orm_dag], session)
        drs = DagRun.find(dag_id=dag.dag_id, session=session)
        assert len(drs) == 1
        dr = drs[0]
        tis = dr.get_task_instances()
        assert len(tis) == 1
        BashOperator(task_id="dummy2", dag=dag, bash_command="echo test")
        SerializedDagModel.write_dag(dag=dag)
        self.scheduler_job._schedule_dag_run(dr, session)
        assert session.query(TaskInstance).filter_by(state=State.SCHEDULED).count() == 2
        session.flush()
        drs = DagRun.find(dag_id=dag.dag_id, session=session)