### 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_DROP_ARCHIVES = Arg(
    ("--drop-archives",),
    help="Drop the archive tables after exporting. Use with caution.",
    action="store_true",
)
ARG_DB_RETRY = Arg(
    ("--retry",),
    default=0,
    type=positive_int(allow_zero=True),
    help="Retry database check upon failure",
)
ARG_DB_RETRY_DELAY = Arg(
    ("--retry-delay",),
    default=1,
    type=positive_int(allow_zero=False),
    help="Wait time between retries in seconds",
)
ARG_POOL_NAME = Arg(("pool",), metavar="NAME", help="Pool name")
ARG_POOL_SLOTS = Arg(("slots",), type=int, help="Pool slots")
ARG_POOL_DESCRIPTION = Arg(("description",), help="Pool description")
ARG_POOL_INCLUDE_DEFERRED = Arg(
    ("--include-deferred",), help="Include deferred tasks in calculations for Pool", action="store_true"
)
ARG_POOL_IMPORT = Arg(
    ("file",),
    metavar="FILEPATH",
    help="Import pools from JSON file. Example format::\n"
    + textwrap.indent(
        textwrap.dedent(