### 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.
"""CustomParser to display help message."""
    def _check_value(self, action, value):
        """Override _check_value and check conditionally added command."""
        if action.choices is not None and value not in action.choices:
            check_legacy_command(action, value)
        super()._check_value(action, value)
    def error(self, message):
        """Override error and use print_instead of print_usage."""
        self.print_help()
        self.exit(2, f"\n{self.prog} command error: {message}, see help above.\n")
_UNSET = object()
class Arg: