Introduce PaginationResult type to return errors in WithPagination methods

[skarimo]

This PR introduces a new type PaginationResult[T any] for results returned by WithPagination methods.

This change was introduced to ensure we forward any errors raised by the goroutine via the channel. Additionally the function signature for WithPagination methods have been changed as well. See below for an example:

	resp, _ := api.ListProcessesWithPagination(ctx, *datadogV2.NewListProcessesOptionalParameters().WithPageLimit(2))
	for paginationResult := range resp {
		if paginationResult.Error != nil {
			fmt.Fprintf(os.Stderr, "Error when calling `ProcessesApi.ListProcesses`: %v\n", paginationResult.Error)
		}
		responseContent, _ := json.MarshalIndent(paginationResult.Item, "", "  ")
		fmt.Fprintf(os.Stdout, "%s\n", responseContent)
	}

[therve]

Looks great! 2 small things:

1. Remove the error from the signature. I think it's useless
2. Update the examples to check for error in the item and print the Item.

I'm wondering how we can document that breaking change. Can you update the PR description as a first step so that we have something to link? Thanks!