### 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)

"""Exports all the variables to the file."""
    _variable_export_helper(args.file)
def _import_helper(filepath):
    """Helps import variables from the file."""
    with open(filepath) as varfile:
        data = varfile.read()
    try:
        var_json = json.loads(data)
    except JSONDecodeError:
        raise SystemExit("Invalid variables file.")
    else:
        suc_count = fail_count = 0
        for k, v in var_json.items():
            try:
                Variable.set(k, v, serialize_json=not isinstance(v, str))
            except Exception as e:
                print(f"Variable import failed: {repr(e)}")
                fail_count += 1
            else:
                suc_count += 1
        print(f"{suc_count} of {len(var_json)} variables successfully updated.")
        if fail_count:
            print(f"{fail_count} variable(s) failed to be updated.")
def _variable_export_helper(filepath):