### 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/www/views.py
"""Customize permission names for FAB's builtin ResetPasswordView."""
    class_permission_name = permissions.RESOURCE_PASSWORD
    method_permission_name = {
        'this_form_get': 'read',
        'this_form_post': 'edit',
    }
    base_permissions = [permissions.ACTION_CAN_EDIT, permissions.ACTION_CAN_READ]
class CustomRoleModelView(RoleModelView):
    """Customize permission names for FAB's builtin RoleModelView."""
    class_permission_name = permissions.RESOURCE_ROLE
    method_permission_name = {
        'delete': 'delete',
        'download': 'read',
        'show': 'read',
        'list': 'read',
        'edit': 'edit',
        'add': 'create',
        'copy_role': 'create',
    }
    base_permissions = [
        permissions.ACTION_CAN_CREATE,
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_EDIT,
        permissions.ACTION_CAN_DELETE,
    ]
class CustomViewMenuModelView(ViewMenuModelView):