**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? -->

files_paths_to_queue = [
            file_path for file_path in file_paths if file_path not in file_paths_to_exclude
        ]
        for file_path, processor in self._processors.items():
            self.log.debug(
                "File path %s is still being processed (started: %s)",
                processor.file_path,
                processor.start_time.isoformat(),
            )
        self.log.debug("Queuing the following files for processing:\n\t%s", "\n\t".join(files_paths_to_queue))
        default = DagFileStat(
            num_dags=0, import_errors=0, last_finish_time=None, last_duration=None, run_count=0
        )
        for file_path in files_paths_to_queue:
            self._file_stats.setdefault(file_path, default)
        self._file_path_queue.extend(files_paths_to_queue)
    def _kill_timed_out_processors(self):
        """Kill any file processors that timeout to defend against process hangs."""
        now = timezone.utcnow()
        processors_to_remove = []
        for file_path, processor in self._processors.items():
            duration = now - processor.start_time
            if duration > self._processor_timeout:
                self.log.error(
                    "Processor for %s with PID %s started at %s has timed out, killing it.",
                    file_path,
                    processor.pid,
                    processor.start_time.isoformat(),
                )