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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def generate_sbi_json(num_pbs: int = 3, project: str = 'sip', programme_block: str = 'sip_demos', pb_config: Union[dict, List[dict]] = None, workflow_config: Union[dict, List[dict]] = None, register_workflows=True) -> str: """Return a JSON string used to configure an SBI."""

    return json.dumps(generate_sbi_config(num_pbs, project, programme_block,
                                          pb_config,
                                          workflow_config, register_workflows))