### 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
"""
    Timer that records duration, and optional sends to statsd backend.
    This class lets us have an accurate timer with the logic in one place (so
    that we don't use datetime math for duration -- it is error prone).
    Example usage:
    .. code-block:: python
        with Stats.timer() as t:
            # Something to time
            frob_the_foos()
        log.info("Frobbing the foos took %.2f", t.duration)
    Or without a context manager:
    .. code-block:: python
        timer = Stats.timer().start()
        # Something to time
        frob_the_foos()
        timer.end()
        log.info("Frobbing the foos took %.2f", timer.duration)
    To send a metric:
    .. code-block:: python
        with Stats.timer("foos.frob"):
            # Something to time
            frob_the_foos()
    Or both:
    .. code-block:: python
        with Stats.timer("foos.frob") as t:
            # Something to time
            frob_the_foos()
        log.info("Frobbing the foos took %.2f", t.duration)
    """