Add "tls' feature workflow and basic test

[rustworthy]

• docker directory in the project's root with the Faktory behind NGINX docker compose set-up;
• update the roundtrip test to conditionally instantiate non-standard streams for Producer and Consumer;
• add tls workflow (the faktory.local.crt was self-signed, and the request was for 358000 days, so that the CI would not fail on it);

Why macos runner excluded?
It's super annoying :( Some runs will go [fine] (https://github.com/jonhoo/faktory-rs/actions/runs/7773048733/job/21196231638), another will fail with network error, or even worse - both will fail with the same connection refused. Also a tweak would be needed in the test like this:

let connector = if cfg!(target_os = "macos") {
            TlsConnector::builder()
                // Danger! Only for testing!
                // On the macos CI runner, the certs are not trusted:
                // { code: -67843, message: "The certificate was not trusted." }
                .danger_accept_invalid_certs(true)
                .build()
                .unwrap()
        } else { /* ..add the server cert to root certs .. */ }

So, not ideal, but staying the ubuntu-latest runner with stable and beta channels tested

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This change is 

[jonhoo]

Nice!

[jonhoo]

Excellent, looks all good to me!

[jonhoo]

Released in 0.12.5 🎉