**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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"""Sleeps until all the processors are done."""
        for processor in self._processors.values():
            while not processor.done:
                time.sleep(0.1)
    def _collect_results_from_processor(self, processor) -> None:
        self.log.debug("Processor for %s finished", processor.file_path)
        Stats.decr("dag_processing.processes", tags={"file_path": processor.file_path, "action": "finish"})
        last_finish_time = timezone.utcnow()
        if processor.result is not None:
            num_dags, count_import_errors = processor.result
        else:
            self.log.error(
                "Processor for %s exited with return code %s.", processor.file_path, processor.exit_code
            )
            count_import_errors = -1
            num_dags = 0
        last_duration = last_finish_time - processor.start_time
        stat = DagFileStat(
            num_dags=num_dags,
            import_errors=count_import_errors,
            last_finish_time=last_finish_time,
            last_duration=last_duration,
            run_count=self.get_run_count(processor.file_path) + 1,
        )
        self._file_stats[processor.file_path] = stat
        file_name = os.path.splitext(os.path.basename(processor.file_path))[0].replace(os.sep, ".")
        Stats.timing(f"dag_processing.last_duration.{file_name}", last_duration)
    def collect_results(self) -> None: