Make the rust hyper client Send so it can be used in rust threads more easily

[wing328]

The hyper client cannot be used easily in threads as it isn't Send friendly. Something like this will fail to compile:

use petstore_hyper::apis::client::APIClient;
use petstore_hyper::apis::configuration::Configuration;

#[tokio::main]
async fn main() {
    tokio::spawn(async move {
        let client = APIClient::new(Configuration::new());
        let _result = client.pet_api().get_pet_by_id(5).await;
    });
}

Issue with more detailed steps to reproduce: #19208

This PR makes the hyper client and its internals Send. So the client can be used in threads.

It ended up being a little larger of a PR in the pursuit of writing a test. It turns out the tests aren't actually being run when invoking verify on the petstore samples. This PR had to touch a few other thing to ensure cargo test would work. Let me know if I should break it up into multiple PRs.

Should I update the pom.xml file to do a cargo test instead of a cargo check? I'm not sure if that was intentional.

Commit summary

This might be a good order to review the changes:

7ee4bca - This is the commit that actually makes the code work in threads. I adds the Send constraint to a bunch generic parameters and traits and uses an Arc instead of an Rc

bda9b6d - This commit adds a test to validate that it works and doesn't regress.

e53c04c - This commit regenerates the samples

The remaining commits were trying to get the tests to run in samples/client/others/rust/ to run successfully. There were several issues to fix to get tests to run successfully.

43ba4f0 46d3520 These set it up so the doc strings are compilable. The first one adds a property called externCrateName cribbing from the rust-server generator. The second one uses the externCrateName and fixes other issues with the example rustdoc examples.

ddb330c The reqwest tests were not compiling and needed a small change.

efbf445 This changes the petstore swagger file and generates the petstore tests to use https. http://petstore.swagger.io/v2 is 301 redirecting to https://petstore.swagger.io/v2 and this is breaking POSTS.
When the client recieves a redirect it does not resend the POST data, instead it switches to GET. This is in line with how browsers behave when encountering a 301 redirect on a POST request, so I wouldn't consider it a bug in the client, but instead a bug in the test code.

Pinging the rust technical committee members: @frol @farcaller @richardwhiuk @paladinzh @jacob-pro

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