**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? -->

return ()
        
        expansion_happened = False
        for schedulable in itertools.chain(schedulable_tis, additional_tis):
            old_state = schedulable.state
            if not schedulable.are_dependencies_met(session=session, dep_context=dep_context):
                old_states[schedulable.key] = old_state
                continue
            
            
            
            
            
            
            new_tis = None
            if schedulable.map_index < 0:
                new_tis = _expand_mapped_task_if_needed(schedulable)
                if new_tis is not None:
                    additional_tis.extend(new_tis)
                    expansion_happened = True
            if new_tis is None and schedulable.state in SCHEDULEABLE_STATES:
                ready_tis.extend(self._revise_map_indexes_if_mapped(schedulable.task, session=session))
                ready_tis.append(schedulable)
        
        tis_filter = TI.filter_for_tis(old_states)
        if tis_filter is not None:
            fresh_tis = session.query(TI).filter(tis_filter).all()
            changed_tis = any(ti.state != old_states[ti.key] for ti in fresh_tis)
        return ready_tis, changed_tis, expansion_happened
    def _are_premature_tis(