
**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
"""Increment stat"""
        if self.allow_list_validator.test(stat):
            tags = tags or []
            return self.dogstatsd.increment(metric=stat, value=count, tags=tags, sample_rate=rate)
        return None
    @validate_stat
    def decr(self, stat, count=1, rate=1, tags=None):
        """Decrement stat"""
        if self.allow_list_validator.test(stat):
            tags = tags or []
            return self.dogstatsd.decrement(metric=stat, value=count, tags=tags, sample_rate=rate)
        return None
    @validate_stat
    def gauge(self, stat, value, rate=1, delta=False, tags=None):  
        """Gauge stat"""
        if self.allow_list_validator.test(stat):
            tags = tags or []
            return self.dogstatsd.gauge(metric=stat, value=value, tags=tags, sample_rate=rate)
        return None
    @validate_stat
    def timing(self, stat, dt, tags=None):
        """Stats timing"""
        if self.allow_list_validator.test(stat):
            tags = tags or []
            return self.dogstatsd.timing(metric=stat, value=dt, tags=tags)
        return None
    @validate_stat
    def timer(self, stat=None, *args, tags=None, **kwargs):