**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? -->

self.dag_id = dag_id
        self.run_id = run_id
        self.execution_date = execution_date
        self.start_date = start_date
        self.external_trigger = external_trigger
        self.conf = conf or {}
        if state is not None:
            self.state = state
        if queued_at is NOTSET:
            self.queued_at = timezone.utcnow() if state == State.QUEUED else None
        else:
            self.queued_at = queued_at
        self.run_type = run_type
        self.dag_hash = dag_hash
        self.creating_job_id = creating_job_id
        super().__init__()
    def __repr__(self):
        return (
            "<DagRun {dag_id} @ {execution_date}: {run_id}, state:{state}, "
            "queued_at: {queued_at}. externally triggered: {external_trigger}>"
        ).format(
            dag_id=self.dag_id,
            execution_date=self.execution_date,
            run_id=self.run_id,
            state=self.state,
            queued_at=self.queued_at,
            external_trigger=self.external_trigger,
        )
    @property
    def logical_date(self) -> datetime: