### 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
"""Returns logger for statsd"""
        
        
        from statsd import StatsClient
        stats_class = conf.getimport('metrics', 'statsd_custom_client_path', fallback=None)
        if stats_class:
            if not issubclass(stats_class, StatsClient):
                raise AirflowConfigException(
                    "Your custom Statsd client must extend the statsd.StatsClient in order to ensure "
                    "backwards compatibility."
                )
            else:
                log.info("Successfully loaded custom Statsd client")
        else:
            stats_class = StatsClient
        statsd = stats_class(
            host=conf.get('metrics', 'statsd_host'),
            port=conf.getint('metrics', 'statsd_port'),
            prefix=conf.get('metrics', 'statsd_prefix'),
        )
        allow_list_validator = AllowListValidator(conf.get('metrics', 'statsd_allow_list', fallback=None))
        return SafeStatsdLogger(statsd, allow_list_validator)
    @classmethod
    def get_dogstatsd_logger(cls):