### Body

The CLI:

`airflow variables set [-h] [-j] [-v] key VALUE`

https://airflow.apache.org/docs/apache-airflow/stable/cli-and-env-variables-ref.html#set_repeat1

Doesn't support adding description though column exists and we support it from Rest API:
https://airflow.apache.org/docs/apache-airflow/stable/stable-rest-api-ref.html#operation/post_variables

**The Task:**

Allow to set description from cli command

### Committer

- [X] I acknowledge that I am a maintainer/committer of the Apache Airflow project.
"""Add this argument to an ArgumentParser."""
        if "metavar" in self.kwargs and "type" not in self.kwargs:
            if self.kwargs["metavar"] == "DIRPATH":
                def type(x):
                    return self._is_valid_directory(parser, x)
                self.kwargs["type"] = type
        parser.add_argument(*self.flags, **self.kwargs)
    def _is_valid_directory(self, parser, arg):
        if not os.path.isdir(arg):
            parser.error(f"The directory '{arg}' does not exist!")
        return arg
def positive_int(*, allow_zero):
    """Define a positive int type for an argument."""
    def _check(value):
        try:
            value = int(value)
            if allow_zero and value == 0:
                return value
            if value > 0:
                return value
        except ValueError:
            pass
        raise argparse.ArgumentTypeError(f"invalid positive int value: '{value}'")
    return _check
def string_list_type(val):