**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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"""
    Timer that records duration, and optional sends to StatsD backend.
    This class lets us have an accurate timer with the logic in one place (so
    that we don't use datetime math for duration -- it is error prone).
    Example usage:
    .. code-block:: python
        with Stats.timer() as t:
            # Something to time
            frob_the_foos()
        log.info("Frobbing the foos took %.2f", t.duration)
    Or without a context manager:
    .. code-block:: python
        timer = Stats.timer().start()
        # Something to time
        frob_the_foos()
        timer.end()
        log.info("Frobbing the foos took %.2f", timer.duration)
    To send a metric:
    .. code-block:: python
        with Stats.timer("foos.frob"):
            # Something to time
            frob_the_foos()
    Or both:
    .. code-block:: python
        with Stats.timer("foos.frob") as t:
            # Something to time
            frob_the_foos()