Consider returning reference type from `AddComponent` API

Start by locating the AddComponent API implementation and any existing coverage for document component registration. Compare its current boolean result with the AddOperationTransformer example, then verify that the returned reference represents the inserted schema while existing registration behavior remains intact.

The AddComponent API currently returns a boolean that indicates if the addition of the component to the document registry succeeded.

It would be nice if the API returned a reference to the item that was just constructed. In an M.A.OpenAPI transformer, I currently need to write:

options.AddOperationTransformer((operation, context, cancellationToken) =>
{
    var schemaService = context.ApplicationServices.GetRequiredKeyedService<IOpenApiSchemaService>(context.DocumentName);
    if (context.Description.RelativePath == "error")
    {
        var errorSchema = schemaService.GetOrCreateSchema(typeof(ProblemDetails));
        context.Document.AddComponent("Error", errorSchema);
        operation.Responses["500"] = new OpenApiResponse
        {
            Description = "Error",
            Content =
            {
                ["application/problem+json"] = new OpenApiMediaType
                {
                    Schema = new OpenApiSchemaReference("Error", context.Document),
                },
            },
        };
    }
    return Task.CompletedTask;
});

but would like to write:

options.AddOperationTransformer((operation, context, cancellationToken) =>
{
    var schemaService = context.ApplicationServices.GetRequiredKeyedService<IOpenApiSchemaService>(context.DocumentName);
    if (context.Description.RelativePath == "error")
    {
        var errorSchema = schemaService.GetOrCreateSchema(typeof(ProblemDetails));
        var insertedSchema = context.Document.AddComponent("Error", errorSchema);
        operation.Responses["500"] = new OpenApiResponse
        {
            Description = "Error",
            Content =
            {
                ["application/problem+json"] = new OpenApiMediaType
                {
                    Schema = insertedSchema,
                },
            },
        };
    }
    return Task.CompletedTask;
});

cc: @baywet I couldn't see if an API that did this existed already and figured I'd add the proposal.