### Description

The stable REST API seems to be missing the functionality to delete a DAG. 
This would mirror clicking the "Trash Can" on the UI (and could maybe eventually power it)

![image](https://user-images.githubusercontent.com/80706212/131702280-2a8d0d74-6388-4b84-84c1-efabdf640cde.png)


### Use case/motivation

_No response_

### Related issues

_No response_

### Are you willing to submit a 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/exceptions.py
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"""Exceptions used by Airflow"""
import datetime
from typing import Any, Dict, List, NamedTuple, Optional
from airflow.utils.code_utils import prepare_code_snippet
from airflow.utils.platform import is_tty
class AirflowException(Exception):
    """
    Base class for all Airflow's errors.
    Each custom exception should be derived from this class
    """
    status_code = 500
class AirflowBadRequest(AirflowException):