Consider switching to back pressure capable API in configurator

[Tvaroh]

Ideally we want to back pressure publisher when it's faster than Korolev is able to render (apply transitions).

[fomkin]

@Tvaroh still actual?

[Tvaroh]

@fomkin up to you I guess. Currently korolev-server does push I believe and nothing can stop it. But maybe it's not an issue.

[fomkin]

@Tvaroh Since Korolev's internals were implemented to Streams it possible to make event handling sequential. We just need to rewrite this code without .runAsyncForget . However a I can't understand why somewho will want such behaviour.