### 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)

ARG_INTERNAL_API_ERROR_LOGFILE = Arg(
    ("-E", "--error-logfile"),
    help="The logfile to store the error log. Use '-' to print to stderr",
)
ARG_INTERNAL_API_ACCESS_LOGFORMAT = Arg(
    ("-L", "--access-logformat"),
    help="The access log format for gunicorn logs",
)
ARG_NUM_RUNS = Arg(
    ("-n", "--num-runs"),
    default=conf.getint("scheduler", "num_runs"),
    type=int,
    help="Set the number of runs to execute before exiting",
)
ARG_DO_PICKLE = Arg(
    ("-p", "--do-pickle"),
    default=False,
    help=(
        "Attempt to pickle the DAG object to send over "
        "to the workers, instead of letting workers run their version "
        "of the code"
    ),
    action="store_true",
)
ARG_WITHOUT_MINGLE = Arg(
    ("--without-mingle",),
    default=False,
    help="Don't synchronize with other workers at start-up",
    action="store_true",
)