Add functionality to easily integrate with DocumentResolvers

[lytedev]

The existing push/pop phases will fail completely if you attempt to integrate them into a DocumentResolver pipeline. It'd be great if a simple way was provided to add similar tracing phases for such situations.

I hope to submit a PR shortly, but my absinthe knowledge is fairly limited, so feedback and discussion on this issue in the meantime would be invaluable. I also may say a number of things that are completely incorrect, so please bear with me!

For example, the existing tracer push/pop phases happen after the Absinthe.Phase.Blueprint and Absinthe.Phase.Document.Result phases. I assume the latter one will remain the same, but is there an analog to Absinthe.Phase.Blueprint when dealing with a DocumentResolver? If so, it shouldn't be overly difficult to add two new push/pop modules (or at least just push) and add an add_document_resolver_phases/1 function that does something similar.

Once that's done, all that needs to be added is a note in the readme that users' DocumentResolver modules should indeed override the pipeline/1 callback and include this new phase-adding function.

Please share any thoughts you might have! Perhaps this entire issue is misguided and I'm missing something obvious, which would actually be wonderful.

Thanks!

[garthk]

I'm having trouble finding references to DocumentResolver. Could you point me to some resources?

[garthk]

If you rebase #14 on #17, will that help show the document resolver in action?

[lytedev]

I'm having trouble finding references to DocumentResolver. Could you point me to some resources?

That's because I used the wrong word! I'm so sorry!

I believe they are referred to as DocumentProviders. Derp.

https://hexdocs.pm/absinthe_plug/Absinthe.Plug.DocumentProvider.html#content

If you rebase #14 on #17, will that help show the document resolver in action?

Probably not. I can attempt to maybe write some tests, but I'm fairly new to both Absinthe and OpenCensus, so it may take some time.

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Let me know if you want me to rename this issue with the correct terminology.