
**Apache Airflow version**:
2.0.0

**Environment**:

- **OS** (e.g. from /etc/os-release): Ubuntu 20.04 LTS
- **Python version**: 3.8
- **Kernel** (e.g. `uname -a`): x86_64 x86_64 x86_64 GNU/Linux 5.4.0-58-generic #64-Ubuntu
- **Install tools**: pip


**What happened**:

Airflow 2.0 does not send metrics to statsD.

I configure Airflow with official documentation (https://airflow.apache.org/docs/apache-airflow/stable/logging-monitoring/metrics.html) and by this article https://dstan.medium.com/run-airflow-statsd-grafana-locally-16b372c86524 (but I used port 8125). 

I turned on statsD:

```ini
statsd_on = True
statsd_host = localhost
statsd_port = 8125
statsd_prefix = airflow
```

But I do not see airflow metrics at http://localhost:9102/metrics (statsD metrics endpoint).

---

P.S. I noticed this error just using Airflow 2.0. In version 1.10.13 everything is ok in the same environment.

Thank you for advance.



airflow/stats.py
"""Get Stat Name Handler from airflow.cfg"""
    return conf.getimport('metrics', 'stat_name_handler') or stat_name_default_handler
T = TypeVar("T", bound=Callable)  
def validate_stat(fn: T) -> T:
    """Check if stat name contains invalid characters.
    Log and not emit stats if name is invalid
    """
    @wraps(fn)
    def wrapper(_self, stat=None, *args, **kwargs):
        try:
            if stat is not None:
                handler_stat_name_func = get_current_handler_stat_name_func()
                stat = handler_stat_name_func(stat)
            return fn(_self, stat, *args, **kwargs)
        except InvalidStatsNameException:
            log.error('Invalid stat name: %s.', stat, exc_info=True)
            return None
    return cast(T, wrapper)
class AllowListValidator: