### 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)

GroupCommand(
        name="variables",
        help="Manage variables",
        subcommands=VARIABLES_COMMANDS,
    ),
    GroupCommand(
        name="jobs",
        help="Manage jobs",
        subcommands=JOBS_COMMANDS,
    ),
    GroupCommand(
        name="db",
        help="Database operations",
        subcommands=DB_COMMANDS,
    ),
    ActionCommand(
        name="kerberos",
        help="Start a kerberos ticket renewer",
        func=lazy_load_command("airflow.cli.commands.kerberos_command.kerberos"),
        args=(
            ARG_PRINCIPAL,
            ARG_KEYTAB,
            ARG_PID,
            ARG_DAEMON,
            ARG_STDOUT,
            ARG_STDERR,
            ARG_LOG_FILE,
            ARG_VERBOSE,
        ),
    ),