### 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.
"\n"
            "The file format is determined by the file extension. "
            "For more information about supported "
            "format, see: https://www.graphviz.org/doc/info/output.html\n"
            "\n"
            "If you want to create a PNG file then you should execute the following command:\n"
            "airflow dags show <DAG_ID> --save output.png\n"
            "\n"
            "If you want to create a DOT file then you should execute the following command:\n"
            "airflow dags show <DAG_ID> --save output.dot\n"
        ),
        func=lazy_load_command("airflow.cli.commands.dag_command.dag_show"),
        args=(
            ARG_DAG_ID,
            ARG_SUBDIR,
            ARG_SAVE,
            ARG_IMGCAT,
            ARG_VERBOSE,
        ),
    ),
    ActionCommand(
        name="show-dependencies",
        help="Displays DAGs with their dependencies",
        description=(
            "The --imgcat option only works in iTerm.\n"
            "\n"
            "For more information, see: https://www.iterm2.com/documentation-images.html\n"
            "\n"
            "The --save option saves the result to the indicated file.\n"
            "\n"