### 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)

"""
            {
                "pool_1": {"slots": 5, "description": "", "include_deferred": true},
                "pool_2": {"slots": 10, "description": "test", "include_deferred": false}
            }"""
        ),
        " " * 4,
    ),
)
ARG_POOL_EXPORT = Arg(("file",), metavar="FILEPATH", help="Export all pools to JSON file")
ARG_VAR = Arg(("key",), help="Variable key")
ARG_VAR_VALUE = Arg(("value",), metavar="VALUE", help="Variable value")
ARG_DEFAULT = Arg(
    ("-d", "--default"), metavar="VAL", default=None, help="Default value returned if variable does not exist"
)
ARG_DESERIALIZE_JSON = Arg(("-j", "--json"), help="Deserialize JSON variable", action="store_true")
ARG_SERIALIZE_JSON = Arg(("-j", "--json"), help="Serialize JSON variable", action="store_true")
ARG_VAR_IMPORT = Arg(("file",), help="Import variables from JSON file")
ARG_VAR_EXPORT = Arg(("file",), help="Export all variables to JSON file")
ARG_PRINCIPAL = Arg(("principal",), help="kerberos principal", nargs="?")
ARG_KEYTAB = Arg(("-k", "--keytab"), help="keytab", nargs="?", default=conf.get("kerberos", "keytab"))
ARG_INTERACTIVE = Arg(
    ("-N", "--interactive"),
    help="Do not capture standard output and error streams (useful for interactive debugging)",
    action="store_true",
)
ARG_FORCE = Arg(
    ("-f", "--force"),
    help="Ignore previous task instance state, rerun regardless if task already succeeded/failed",
    action="store_true",