Add examples to AddOpenApi extension method/overloads

[mikekistler]

Add examples to AddOpenApi extension method/overloads

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Adds examples to the xmldoc for the AddOpenApi extension methods/overloads.

Description

Added an example to the xmldoc of each method showing the most common usage of this extension method -- to add OpenAPI services to the service collection of WebApplicationBuilder.

[captainsafia]

The build is having trouble resolving the WebApplicationBuilder reference.

We'll need to add a reference to the Microsoft.AspNetCore.DefaultBuilder project to the *.csproj for this library then add any necessary usings.

[captainsafia]

Here and elsewhere?

Suggested change

	/// This method is commonly used to add OpenAPI services to the service collection of a
	/// This method is commonly used to add OpenAPI services to the <see cref="IServiceCollection" /> of a