### 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_PORT = Arg(
    ("-p", "--port"),
    default=conf.get("webserver", "WEB_SERVER_PORT"),
    type=int,
    help="The port on which to run the server",
)
ARG_SSL_CERT = Arg(
    ("--ssl-cert",),
    default=conf.get("webserver", "WEB_SERVER_SSL_CERT"),
    help="Path to the SSL certificate for the webserver",
)
ARG_SSL_KEY = Arg(
    ("--ssl-key",),
    default=conf.get("webserver", "WEB_SERVER_SSL_KEY"),
    help="Path to the key to use with the SSL certificate",
)
ARG_WORKERS = Arg(
    ("-w", "--workers"),
    default=conf.get("webserver", "WORKERS"),
    type=int,
    help="Number of workers to run the webserver on",
)
ARG_WORKERCLASS = Arg(
    ("-k", "--workerclass"),
    default=conf.get("webserver", "WORKER_CLASS"),
    choices=["sync", "eventlet", "gevent", "tornado"],
    help="The worker class to use for Gunicorn",
)
ARG_WORKER_TIMEOUT = Arg(
    ("-t", "--worker-timeout"),