### 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_WITHOUT_GOSSIP = Arg(
    ("--without-gossip",),
    default=False,
    help="Don't subscribe to other workers events",
    action="store_true",
)
ARG_TASK_PARAMS = Arg(("-t", "--task-params"), help="Sends a JSON params dict to the task")
ARG_POST_MORTEM = Arg(
    ("-m", "--post-mortem"), action="store_true", help="Open debugger on uncaught exception"
)
ARG_ENV_VARS = Arg(
    ("--env-vars",),
    help="Set env var in both parsing time and runtime for each of entry supplied in a JSON dict",
    type=json.loads,
)
ARG_CONN_ID = Arg(("conn_id",), help="Connection id, required to get/add/delete/test a connection", type=str)
ARG_CONN_ID_FILTER = Arg(
    ("--conn-id",), help="If passed, only items with the specified connection ID will be displayed", type=str
)
ARG_CONN_URI = Arg(
    ("--conn-uri",), help="Connection URI, required to add a connection without conn_type", type=str
)
ARG_CONN_JSON = Arg(
    ("--conn-json",), help="Connection JSON, required to add a connection using JSON representation", type=str
)
ARG_CONN_TYPE = Arg(
    ("--conn-type",), help="Connection type, required to add a connection without conn_uri", type=str
)
ARG_CONN_DESCRIPTION = Arg(
    ("--conn-description",), help="Connection description, optional when adding a connection", type=str