
**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
"""Start the timer"""
        if self.real_timer:
            self.real_timer.start()
        self._start_time = time.perf_counter()
        return self
    def stop(self, send=True):  
        """Stop the timer, and optionally send it to stats backend"""
        self.duration = time.perf_counter() - self._start_time
        if send and self.real_timer:
            self.real_timer.stop()
class DummyStatsLogger:
    """If no StatsLogger is configured, DummyStatsLogger is used as a fallback"""
    @classmethod
    def incr(cls, stat, count=1, rate=1):
        """Increment stat"""
    @classmethod
    def decr(cls, stat, count=1, rate=1):
        """Decrement stat"""
    @classmethod
    def gauge(cls, stat, value, rate=1, delta=False):
        """Gauge stat"""
    @classmethod
    def timing(cls, stat, dt):
        """Stats timing"""
    @classmethod
    def timer(cls, *args, **kwargs):
        """Timer metric that can be cancelled"""
        return Timer()
ALLOWED_CHARACTERS = set(string.ascii_letters + string.digits + '_.-')
def stat_name_default_handler(stat_name, max_length=250) -> str: