### 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)

"airflow connections export - --file-format yaml\n"
            "The --file-format parameter can also be used for the files, for example:\n"
            "airflow connections export /tmp/connections --file-format json.\n"
            "When exporting in `env` file format, you control whether URI format or JSON format "
            "is used to serialize the connection by passing `uri` or `json` with option "
            "`--serialization-format`.\n"
        ),
        func=lazy_load_command("airflow.cli.commands.connection_command.connections_export"),
        args=(
            ARG_CONN_EXPORT,
            ARG_CONN_EXPORT_FORMAT,
            ARG_CONN_EXPORT_FILE_FORMAT,
            ARG_CONN_SERIALIZATION_FORMAT,
            ARG_VERBOSE,
        ),
    ),
    ActionCommand(
        name="import",
        help="Import connections from a file",
        description=(
            "Connections can be imported from the output of the export command.\n"
            "The filetype must by json, yaml or env and will be automatically inferred."
        ),
        func=lazy_load_command("airflow.cli.commands.connection_command.connections_import"),
        args=(
            ARG_CONN_IMPORT,
            ARG_CONN_OVERWRITE,
            ARG_VERBOSE,
        ),
    ),