feat: add overload IncludeMagicOnionXmlComments

[arika0093]

Swashbuckle's IncludeXmlComments has overloads such as the following:
https://github.com/domaindrivendev/Swashbuckle.AspNetCore/blob/8f82acf800a8733a389328177d258186e947c20d/src/Swashbuckle.AspNetCore.SwaggerGen/DependencyInjection/SwaggerGenOptionsExtensions.cs#L839-L847

Furthermore, this overload is also used in the documentation.
https://github.com/domaindrivendev/Swashbuckle.AspNetCore/blob/8f82acf800a8733a389328177d258186e947c20d/docs/configure-and-customize-swaggergen.md?plain=1#L257

What it does is exactly the same as the current sample, but I personally prefer specifying the assembly as an argument (it requires slightly less typing). I'm also accustomed to this approach from Swashbuckle.

Therefore, I added an overload to the IncludeMagicOnionXmlComments method that allows specifying an assembly, similar to Swashbuckle's IncludeXmlComments.

I've also updated the documentation to use this overload. (Though the original code might be preferable in documentation, as it explicitly shows loading the XML file.)

Thanks for the great library!

[mayuki]

Thank you for contribution. Looks good to me!