### 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_MARK_SUCCESS = Arg(
    ("-m", "--mark-success"), help="Mark jobs as succeeded without running them", action="store_true"
)
ARG_INCLUDE_DESCRIPTIONS = Arg(
    ("-d", "--include-descriptions"),
    help="Show descriptions for the configuration variables",
    action="store_true",
)
ARG_INCLUDE_EXAMPLES = Arg(
    ("-e", "--include-examples"), help="Show examples for the configuration variables", action="store_true"
)
ARG_INCLUDE_SOURCES = Arg(
    ("-s", "--include-sources"), help="Show source of the configuration variable", action="store_true"
)
ARG_INCLUDE_ENV_VARS = Arg(
    ("-V", "--include-env-vars"), help="Show environment variable for each option", action="store_true"
)
ARG_COMMENT_OUT_EVERYTHING = Arg(
    ("-c", "--comment-out-everything"),
    help="Comment out all configuration options. Useful as starting point for new installation",
    action="store_true",
)
ARG_EXCLUDE_PROVIDERS = Arg(
    ("-p", "--exclude-providers"),
    help="Exclude provider configuration (they are included by default)",
    action="store_true",
)
ARG_DEFAULTS = Arg(
    ("-a", "--defaults"),
    help="Show only defaults - do not include local configuration, sources,"