### 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_DB_VERSION__DOWNGRADE = Arg(
    ("-n", "--to-version"),
    help="(Optional) If provided, only run migrations up to this version.",
)
ARG_DB_FROM_VERSION = Arg(
    ("--from-version",),
    help="(Optional) If generating sql, may supply a *from* version",
)
ARG_DB_REVISION__DOWNGRADE = Arg(
    ("-r", "--to-revision"),
    help="The Alembic revision to downgrade to. Note: must provide either `--to-revision` or `--to-version`.",
)
ARG_DB_FROM_REVISION = Arg(
    ("--from-revision",),
    help="(Optional) If generating sql, may supply a *from* Alembic revision",
)
ARG_DB_SQL_ONLY = Arg(
    ("-s", "--show-sql-only"),
    help="Don't actually run migrations; just print out sql scripts for offline migration. "
    "Required if using either `--from-revision` or `--from-version`.",
    action="store_true",
    default=False,
)
ARG_DB_SKIP_INIT = Arg(
    ("-s", "--skip-init"),
    help="Only remove tables; do not perform db init.",
    action="store_true",
    default=False,
)