WIP: Replace httpc with gun

[SimonUnge]

Add put API

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[the-mikedavis]

Instead of synchronously awaiting the replies we should try to use gun's async API https://ninenines.eu/docs/en/gun/2.2/manual/gun_response/

With that we can avoid blocking this gen_server: we can start the request with gun:post/gun:get/..., store the StreamRef in state and and in the handle_call/3 impl return {noreply, State}. Then once the {gun_response, ..} message arrives we can use gen_server:reply/2 to notify the caller. Then the gen_server can start other requests as other requests are in-flight.

This would be a big improvement over httpc:request/4 since that is always synchronous

[SimonUnge]

Oh, good idea.

[lukebakken]

Can the functions in rabbitmq_aws actually benefit from this though?

[the-mikedavis]

Currently this gen_server blocks for any request so you can't download two files from S3 for example in parallel. It could also make sense to get rid of this server or change it so it's only in charge of refreshing credentials. Then callers could interact with the gun connection processes directly without the extra hop to this server first

[michaelklishin]

@SimonUnge if you don't need the branch any more, can you please delete it? Thank you.