### 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)

type=string_lower_type,
    choices=["json", "uri"],
)
ARG_CONN_IMPORT = Arg(("file",), help="Import connections from a file")
ARG_CONN_OVERWRITE = Arg(
    ("--overwrite",),
    help="Overwrite existing entries if a conflict occurs",
    required=False,
    action="store_true",
)
ARG_PROVIDER_NAME = Arg(
    ("provider_name",), help="Provider name, required to get provider information", type=str
)
ARG_FULL = Arg(
    ("-f", "--full"),
    help="Full information about the provider, including documentation information.",
    required=False,
    action="store_true",
)
ARG_USERNAME = Arg(("-u", "--username"), help="Username of the user", required=True, type=str)
ARG_USERNAME_OPTIONAL = Arg(("-u", "--username"), help="Username of the user", type=str)
ARG_FIRSTNAME = Arg(("-f", "--firstname"), help="First name of the user", required=True, type=str)
ARG_LASTNAME = Arg(("-l", "--lastname"), help="Last name of the user", required=True, type=str)
ARG_ROLE = Arg(
    ("-r", "--role"),
    help="Role of the user. Existing roles include Admin, User, Op, Viewer, and Public",
    required=True,
    type=str,
)
ARG_EMAIL = Arg(("-e", "--email"), help="Email of the user", required=True, type=str)