PDF Generation for Products with Special Characters in Brand Names

I encountered an issue while generating PDFs where some product brand names include special characters like &. To temporarily resolve this, I used .Replace("&", "**& ;**") in the [FooterHtml property of Markdown2PdfOptions](https://github.com/dotnet/eShopSupport/blob/main/seeddata/DataGenerator/Generators/ManualPdfConverter.cs#L35).

For a permanent fix, we can:

Update the Prompt: Adjust the product generation prompt to avoid names with special characters.
Use WebUtility.HtmlEncode: Automatically escape special characters (e.g., &, <, >) using WebUtility.HtmlEncode to handle them correctly in XML/HTML contexts.