OKHTTP3 library is out of date.

[epachamo]

• [x ] I have searched open and closed issues for duplicates
• [x ] I am submitting a bug report for existing functionality that does not work as intended
• [x ] I have read https://github.com/signalapp/Signal-Android/wiki/Submitting-useful-bug-reports
• [x ] This isn't a feature request or a discussion topic

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Bug description

The current version of OKHttp is 3. This should be upgraded to OKHttp 4, as version 3 hasn't received an update in almost 4 years now.

Upgrading is easy, I forked signal, made the mostly syntactic changes myself, ran the tests successfully. Upgrade instructions are given here by the library maintainers:

https://square.github.io/okhttp/changelogs/upgrading_to_okhttp_4/

[nicholas-signal]

We had tried to perform the 3 -> 4 upgrade back in Signal 6.32, but it caused deadlocks inside our CI pipeline. We hope to revisit it eventually.