Prefix filename with ISO8601 creation date in UTC timezone

[huyz]

Based on #623, I wanted an ISO8601 timestamp in the UTC timezone (for brevity and consistency regardless of where I am in the world at the time):

<%*
    const format = "YYYY-MM-DDTHHmmSSZZ";
    const creationDate = tp.file.creation_date(format);
    const id = new moment(creationDate, format).utc().format("YYYY-MM-DDTHHmmSS[Z]")
    await tp.file.rename(`${id} ${tp.file.title}`);
%>