### 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)

action="store_true",
    default=False,
)
ARG_OUTPUT = Arg(
    (
        "-o",
        "--output",
    ),
    help="Output format. Allowed values: json, yaml, plain, table (default: table)",
    metavar="(table, json, yaml, plain)",
    choices=("table", "json", "yaml", "plain"),
    default="table",
)
ARG_COLOR = Arg(
    ("--color",),
    help="Do emit colored output (default: auto)",
    choices={ColorMode.ON, ColorMode.OFF, ColorMode.AUTO},
    default=ColorMode.AUTO,
)
ARG_VERSION_RANGE = Arg(
    ("-r", "--range"),
    help="Version range(start:end) for offline sql generation. Example: '2.0.2:2.2.3'",
    default=None,
)
ARG_REVISION_RANGE = Arg(
    ("--revision-range",),
    help=(
        "Migration revision range(start:end) to use for offline sql generation. "
        "Example: ``a13f7613ad25:7b2661a43ba3``"
    ),