**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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"""Returns the dag_director as a string."""
        if isinstance(self._dag_directory, Path):
            return str(self._dag_directory.resolve())
        else:
            return str(self._dag_directory)
    def set_file_paths(self, new_file_paths):
        """
        Update this with a new set of paths to DAG definition files.
        :param new_file_paths: list of paths to DAG definition files
        :return: None
        """
        self._file_paths = new_file_paths
        self._file_path_queue = collections.deque(x for x in self._file_path_queue if x in new_file_paths)
        
        filtered_processors = {}
        for file_path, processor in self._processors.items():
            if file_path in new_file_paths:
                filtered_processors[file_path] = processor
            else:
                self.log.warning("Stopping processor for %s", file_path)
                Stats.decr("dag_processing.processes", tags={"file_path": file_path, "action": "stop"})
                processor.terminate()
                self._file_stats.pop(file_path)
        to_remove = set(self._file_stats.keys()) - set(self._file_paths)
        for key in to_remove:
            
            del self._file_stats[key]
        self._processors = filtered_processors
    def wait_until_finished(self):