### 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
"""Raise when multiple values are found for the same conn_id"""
class TaskDeferred(BaseException):
    """
    Special exception raised to signal that the operator it was raised from
    wishes to defer until a trigger fires.
    """
    def __init__(
        self,
        *,
        trigger,
        method_name: str,
        kwargs: Optional[Dict[str, Any]] = None,
        timeout: Optional[datetime.timedelta] = None,
    ):
        super().__init__()
        self.trigger = trigger
        self.method_name = method_name
        self.kwargs = kwargs
        self.timeout = timeout
        
        if self.timeout is not None and not hasattr(self.timeout, "total_seconds"):
            raise ValueError("Timeout value must be a timedelta")
    def __repr__(self) -> str:
        return f"<TaskDeferred trigger={self.trigger} method={self.method_name}>"
class TaskDeferralError(AirflowException):
    """Raised when a task failed during deferral for some reason."""