feature: Allow to pass server configuration

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By default Renderer server run at first free port after 8000, this MR allows plugin to configure server port via prerender.serverConfig

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Hi @ABuffSeagull,

I'd like to notice, that I'm unable to successfully run test suite on master branch (as well as my fork), so I cannot verify that my change will run well. It should but in case you found out any issues with implementation, I'll glad to fix them.

[ABuffSeagull]

Yeah, the tests have always been super flaky, I need to see if I can harden them up. But thank you, I'll look into this when I get the chance