### 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)

args=(ARG_VAR_IMPORT, ARG_VERBOSE),
    ),
    ActionCommand(
        name="export",
        help="Export all variables",
        func=lazy_load_command("airflow.cli.commands.variable_command.variables_export"),
        args=(ARG_VAR_EXPORT, ARG_VERBOSE),
    ),
)
DB_COMMANDS = (
    ActionCommand(
        name="init",
        help=(
            "Deprecated -- use `migrate` instead. "
            "To create default connections use `airflow connections create-default-connections`. "
            "Initialize the metadata database"
        ),
        func=lazy_load_command("airflow.cli.commands.db_command.initdb"),
        args=(ARG_VERBOSE,),
        hide=True,
    ),
    ActionCommand(
        name="check-migrations",
        help="Check if migration have finished",
        description="Check if migration have finished (or continually check until timeout)",
        func=lazy_load_command("airflow.cli.commands.db_command.check_migrations"),
        args=(ARG_MIGRATION_TIMEOUT, ARG_VERBOSE),
    ),
    ActionCommand(
        name="reset",