### Apache Airflow version

2.1.2

### Operating System

Gentoo/Linux

### Versions of Apache Airflow Providers

_No response_

### Deployment

Docker-Compose

### Deployment details

_No response_

### What happened

In datadog-agent logs, got parsing error

[ AGENT ] 2021-09-29 03:20:01 UTC | CORE | ERROR | (pkg/dogstatsd/server.go:411 in errLog) | Dogstatsd: error parsing metric message '"airflow.dagrun.schedule_delay.skew:<Period [2021-09-29T03:20:00+00:00 -> 2021-09-29T03:20:00.968404+00:00]>|ms"': could not parse dogstatsd metric value: strconv.ParseFloat: parsing "<Period [2021-09-29T03:20:00+00:00 -> 2021-09-29T03:20:00.968404+00:00]>": invalid syntax

### What you expected to happen

since datadog agent expects a float, see https://github.com/DataDog/datadog-agent/blob/6830beaeb182faadac40368d9d781b796b4b2c6f/pkg/dogstatsd/parse.go#L119, the schedule_delay should be a float instead of timedelta.

### How to reproduce

_No response_

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)

airflow/stats.py
factory = None
    instance: Optional[StatsLogger] = None
    def __getattr__(cls, name):
        if not cls.instance:
            try:
                cls.instance = cls.factory()
            except (socket.gaierror, ImportError) as e:
                log.error("Could not configure StatsClient: %s, using DummyStatsLogger instead.", e)
                cls.instance = DummyStatsLogger()
        return getattr(cls.instance, name)
    def __init__(cls, *args, **kwargs):
        super().__init__(cls)
        if cls.__class__.factory is None:
            is_datadog_enabled_defined = conf.has_option('metrics', 'statsd_datadog_enabled')
            if is_datadog_enabled_defined and conf.getboolean('metrics', 'statsd_datadog_enabled'):
                cls.__class__.factory = cls.get_dogstatsd_logger
            elif conf.getboolean('metrics', 'statsd_on'):
                cls.__class__.factory = cls.get_statsd_logger
            else:
                cls.__class__.factory = DummyStatsLogger
    @classmethod
    def get_statsd_logger(cls):