Experimentally support practical size specification such as A4, B0, introducing PdfSize.

[fummicc1]

• Issue: [csv2img]: Customise colours and size of PDF #43

• from now, we can set Pdf output size with csv.update(pdfMetadata:) method !

        await csv.update(
            pdfMetadata: .init(
                size: .a4,
                orientation: .landscape
            )
        )