[2/2] Update ApolloPagination usage docs for a 0.2.0 release

[Iron-Ham]

Depends on #316
Depends on #292

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This pull request updates the usage guide related to the changes made in #292.

Note that I cannot create or point at a Pagination-0.2.0 branch (nor can I point at #316 and still have this PR appear in this repo), but this would be part 2 of 2 for updating the docs for a 0.2.0 release. To that end, I recommend ignoring the total diff and looking at the relevant commit of this pull request.

Perhaps something to consider for general docs after 0.2.0 is out: we should include usage docs for the AsyncGraphQLQueryPager, as we make mention of it, but never showcase its usage.

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[AnthonyMDev]

Do any of the code samples in the docs need to be updated for these changes?

[Iron-Ham]

No. I think the fact that they don't implies the need for more robust docs. Adding it to my to-do list ☺️

EDIT:

• Found that the existing docs made references to callbacks that weren't there (although, existing docs never used them).
• Added some extra notes on AsyncGraphQLQueryPager

I think one of the big impediments is likely a good usage sample for both UIKit and SwiftUI. I have one up for SwiftUI here, but ideally I'd want to snap away all of the known issues prior to pushing for an official sample or going 1.0. The need for a secondary trigger... is one that I'd have to spend a lot of time thinking about – and I wonder if that's something that you'd be open to discussing in a Zoom chat @AnthonyMDev? It's a tough one to contend with, as the current API design is meant to prevent the issue of fetching a next page based on cached data – which is good.

Perhaps a mechanism for queuing one pagination operation may be a good thing, as @mapy1874 alluded to in apollographql/apollo-ios#3349. I can take some time tomorrow to noodle on a potential solution.