Modernize hosting-model code snippets in file-uploads.md to minimal hosting

[SkyDevLab]

Fixes #37641

Summary

Modernizes older pre-3.0 hosting snippets in the Server and app configuration section of aspnetcore/mvc/models/file-uploads.md (>= aspnetcore-6.0 moniker block) to minimal hosting style, aligning with the snippets introduced in #37600 and the rest of the modern documentation:

• Updated Multipart body length limit services.Configure<FormOptions> to builder.Services.Configure<FormOptions> and updated prose from Startup.ConfigureServices to Program.cs.
• Updated Multipart body length limit Razor Pages convention example to builder.Services.AddRazorPages(options => ...) in Program.cs.
• Updated Kestrel maximum request body size CreateHostBuilder / ConfigureWebHostDefaults / webBuilder.ConfigureKestrel / .UseStartup<Startup>() snippet to builder.WebHost.ConfigureKestrel(options => ...) in Program.cs.
• Updated Kestrel maximum request body size Razor Pages convention example to builder.Services.AddRazorPages(options => ...) in Program.cs.
• Bumped ms.date to 10/03/2026.

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aspnetcore/mvc/models/file-uploads.md	Learn preview

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[guardrex]

Thanks, @SkyDevLab! I'll review this on Monday morning. Have a great weekend! 🏖️🎉

[guardrex]

Thanks @SkyDevLab! 🚀 I'll get this merged into the live article by EOD.