### 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_CONN_HOST = Arg(("--conn-host",), help="Connection host, optional when adding a connection", type=str)
ARG_CONN_LOGIN = Arg(("--conn-login",), help="Connection login, optional when adding a connection", type=str)
ARG_CONN_PASSWORD = Arg(
    ("--conn-password",), help="Connection password, optional when adding a connection", type=str
)
ARG_CONN_SCHEMA = Arg(
    ("--conn-schema",), help="Connection schema, optional when adding a connection", type=str
)
ARG_CONN_PORT = Arg(("--conn-port",), help="Connection port, optional when adding a connection", type=str)
ARG_CONN_EXTRA = Arg(
    ("--conn-extra",), help="Connection `Extra` field, optional when adding a connection", type=str
)
ARG_CONN_EXPORT = Arg(
    ("file",),
    help="Output file path for exporting the connections",
    type=argparse.FileType("w", encoding="UTF-8"),
)
ARG_CONN_EXPORT_FORMAT = Arg(
    ("--format",),
    help="Deprecated -- use `--file-format` instead. File format to use for the export.",
    type=str,
    choices=["json", "yaml", "env"],
)
ARG_CONN_EXPORT_FILE_FORMAT = Arg(
    ("--file-format",), help="File format for the export", type=str, choices=["json", "yaml", "env"]
)
ARG_CONN_SERIALIZATION_FORMAT = Arg(
    ("--serialization-format",),
    help="When exporting as `.env` format, defines how connections should be serialized. Default is `uri`.",