### 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)

"""Adds new connection."""
    has_uri = bool(args.conn_uri)
    has_json = bool(args.conn_json)
    has_type = bool(args.conn_type)
    
    try:
        helpers.validate_key(args.conn_id, max_length=200)
    except Exception as e:
        raise SystemExit(f"Could not create connection. {e}")
    if not has_type and not (has_json or has_uri):
        raise SystemExit("Must supply either conn-uri or conn-json if not supplying conn-type")
    if has_json and has_uri:
        raise SystemExit("Cannot supply both conn-uri and conn-json")
    if has_type and args.conn_type not in _get_connection_types():
        warnings.warn(f"The type provided to --conn-type is invalid: {args.conn_type}")
        warnings.warn(
            f"Supported --conn-types are:{_get_connection_types()}."
            "Hence overriding the conn-type with generic"
        )
        args.conn_type = "generic"