### 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.
"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-dependencies --save output.png\n"
            "\n"
            "If you want to create a DOT file then you should execute the following command:\n"
            "airflow dags show-dependencies --save output.dot\n"
        ),
        func=lazy_load_command("airflow.cli.commands.dag_command.dag_dependencies_show"),
        args=(
            ARG_SUBDIR,
            ARG_SAVE,
            ARG_IMGCAT,
            ARG_VERBOSE,
        ),
    ),
    ActionCommand(
        name="backfill",
        help="Run subsections of a DAG for a specified date range",
        description=(
            "Run subsections of a DAG for a specified date range. If reset_dag_run option is used, "
            "backfill will first prompt users whether airflow should clear all the previous dag_run and "
            "task_instances within the backfill date range. If rerun_failed_tasks is used, backfill "
            "will auto re-run the previous failed task instances  within the backfill date range"
        ),
        func=lazy_load_command("airflow.cli.commands.dag_command.dag_backfill"),
        args=(
            ARG_DAG_ID,