How to use the flowclient.get_available_dates function in flowclient

cdr_types : list of str, optional
        Subset of CDR types for which to find available dates.
        If not provided, the union of available dates for all CDR types will be returned.
    
    Returns
    -------
    list of pendulum.Date
        List of available dates, in chronological order
    """
    prefect.context.logger.info(
        f"Getting available dates from FlowAPI at '{prefect.config.flowapi_url}'."
    )
    conn = flowclient.connect(
        url=prefect.config.flowapi_url, token=environ["FLOWAPI_TOKEN"]
    )
    dates = flowclient.get_available_dates(connection=conn)
    prefect.context.logger.debug(f"Available dates: {dates}")
    if cdr_types is None:
        prefect.context.logger.debug(
            "No CDR types provided. Will return available dates for all CDR types."
        )
        cdr_types = dates.keys()
    else:
        prefect.context.logger.debug(
            f"Returning available dates for CDR types {cdr_types}."
        )
        unknown_cdr_types = set(cdr_types).difference(dates.keys())
        if unknown_cdr_types:
            warnings.warn(f"No data available for CDR types {unknown_cdr_types}.")
    dates_union = set.union(
        *[
            set(pendulum.parse(date, exact=True) for date in dates[cdr_type])