Support images, .NET 8.0 and added options

[ArjanKw]

Created a fork as I needed to create images with wkhtmltoimage in .NET 8.

• Add .NET 8 support;
• Support Partial views (return new ViewAsPdf("MyPartialView", isPartialView = true);
• Added ViewAsImage based on original Rotativa code;
• Refactored ViewAsPdf: use default ViewName, Model, ViewData and TempData properties instead of overriding them;
• Removed MasterName as it wasn't used;
• Added the zoom parameter (as #54 has conflicts);
• Fixed the tests by upgrading the deprecated iTextSharp to itext7.
• Added option to specify whether you want a Base URL to be added to the head in the HTML (fix for #88 ).