### Description

Currently, the `airflow variables export` command requires an explicit file path and does not support output to stdout. However connections can be printed to stdout using `airflow connections export -`. This inconsistency between the two export commands can lead to confusion and limits the flexibility of the variables export command.

### Use case/motivation

To bring some consistency, similar to connections, variables should also be printed to STDOUT, using `-` instead of filename. 

### Related issues

_No response_

### Are you willing to submit a PR?

- [X] 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)

help="Rotate encrypted connection credentials and variables",
        description=(
            "Rotate all encrypted connection credentials and variables; see "
            "https://airflow.apache.org/docs/apache-airflow/stable/howto/secure-connections.html"
            "#rotating-encryption-keys"
        ),
        args=(),
    ),
    GroupCommand(name="config", help="View configuration", subcommands=CONFIG_COMMANDS),
    ActionCommand(
        name="info",
        help="Show information about current Airflow and environment",
        func=lazy_load_command("airflow.cli.commands.info_command.show_info"),
        args=(
            ARG_ANONYMIZE,
            ARG_FILE_IO,
            ARG_VERBOSE,
            ARG_OUTPUT,
        ),
    ),
    ActionCommand(
        name="plugins",
        help="Dump information about loaded plugins",
        func=lazy_load_command("airflow.cli.commands.plugins_command.dump_plugins"),
        args=(ARG_OUTPUT, ARG_VERBOSE),
    ),
    ActionCommand(
        name="standalone",
        help="Run an all-in-one copy of Airflow",
        func=lazy_load_command("airflow.cli.commands.standalone_command.standalone"),