Make WPT horizontally scalable

[pmeenan]

When distributed reliable queues are available, it should be possible to submit a test to any of multiple entry points, have an agent run the test and upload the result as a single POST back (which would include an opaque blob with all of the test data).

That way the receiving server can construct and archive the test result into cloud storage without needing any distributed state.

Any end-point can then display the test when it is polled for the result by restoring from the archive.

In principle, it should also be possible to post a message containing the JSON version of the testresult data into a queue for notification to the client without needing to restore the entire test.

[github-actions]

We're in the process of cleaning up issues on this project in order to ensure we're able to stay on top of high priority bugs and feature requests. As a part of this process, we're automatically closing any issues that have had no activity within the last two years, including this one, since the codebase has changed dramatically in that time. If you feel this is still relevant, please file a new issue using the relevant issue template so we can get it prioritized. Thanks!