### 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
"""Get DataDog statsd logger"""
        from datadog import DogStatsd
        dogstatsd = DogStatsd(
            host=conf.get('metrics', 'statsd_host'),
            port=conf.getint('metrics', 'statsd_port'),
            namespace=conf.get('metrics', 'statsd_prefix'),
            constant_tags=cls.get_constant_tags(),
        )
        dogstatsd_allow_list = conf.get('metrics', 'statsd_allow_list', fallback=None)
        allow_list_validator = AllowListValidator(dogstatsd_allow_list)
        return SafeDogStatsdLogger(dogstatsd, allow_list_validator)
    @classmethod
    def get_constant_tags(cls):
        """Get constant DataDog tags to add to all stats"""
        tags = []
        tags_in_string = conf.get('metrics', 'statsd_datadog_tags', fallback=None)
        if tags_in_string is None or tags_in_string == '':
            return tags
        else:
            for key_value in tags_in_string.split(','):
                tags.append(key_value)
            return tags
if TYPE_CHECKING:
    Stats: StatsLogger
else:
    class Stats(metaclass=_Stats):
        """Empty class for Stats - we use metaclass to inject the right one"""