PDF导出扩展

现在的PdfExporterAttribute很多打印属性无法自定义。比如根据实例属性设置不同的页眉页脚等
ps：下面代码临时凑活的，命名需要规范。

接口或抽象类
``` c#
public abstract class ICustomPdfExporter
{
public virtual void Configure(ref ObjectSettings o)
{

}
}

```

导出pdf时获取下
``` c#

public async Task ExportBytesByTemplateEx(T data, string template) where T : class
{
var html = await _htmlExporter.ExportByTemplate(data, template);
var pdfAttr = data.GetType().GetCustomAttribute() ?? new();

var objSettings = new ObjectSettings
{
HtmlContent = html,
Encoding = Encoding.UTF8,
PagesCount = pdfAttr.IsEnablePagesCount ? true : (bool?)null,
WebSettings = { DefaultEncoding = Encoding.UTF8.BodyName },
};
if (pdfAttr.HeaderSettings != null)
objSettings.HeaderSettings = pdfAttr.HeaderSettings;

if (pdfAttr.FooterSettings != null)
objSettings.FooterSettings = pdfAttr?.FooterSettings;

// 增加 复写打印设置
if (data is ICustomPdfExporter data1)
{
data1.Configure(ref objSettings);
}

var htmlToPdfDocument = new HtmlToPdfDocument
{
GlobalSettings =
{
PaperSize = pdfAttr!.PaperKind == PaperKind.Custom
? pdfAttr.PaperSize : pdfAttr.PaperKind,
Orientation = pdfAttr.Orientation,
ColorMode = ColorMode.Color,
DocumentTitle = pdfAttr.Name,
},
Objects =
{
objSettings
}
};

if (pdfAttr.MarginSettings != null)
{
htmlToPdfDocument.GlobalSettings.Margins = pdfAttr.MarginSettings;
}

return PdfConverter.Convert(htmlToPdfDocument);

}
```