
**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
"""Class to filter unwanted stats"""
    def __init__(self, allow_list=None):
        if allow_list:
            
            self.allow_list = tuple([item.strip().lower() for item in allow_list.split(',')])
        else:
            self.allow_list = None
    def test(self, stat):
        """Test if stat is in the Allow List"""
        if self.allow_list is not None:
            return stat.strip().lower().startswith(self.allow_list)
        else:
            return True  
class SafeStatsdLogger:
    """Statsd Logger"""
    def __init__(self, statsd_client, allow_list_validator=AllowListValidator()):
        self.statsd = statsd_client
        self.allow_list_validator = allow_list_validator
    @validate_stat
    def incr(self, stat, count=1, rate=1):
        """Increment stat"""
        if self.allow_list_validator.test(stat):
            return self.statsd.incr(stat, count, rate)
        return None
    @validate_stat
    def decr(self, stat, count=1, rate=1):