Runtime Config Independent of Serialization

[rylev]

This change makes runtime config completely independent of how (or even if) it is serialized. The advantage of this is that we are no longer imposing toml of runtimes while still providing convenient handling of toml for runtimes that want to handle runtime config with toml.

RuntimeFactors gains an associated type RuntimeConfig which is passed directly to RuntimeFactors::configure_app. The derive macro ensures that this RuntimeConfig type implements FactorRuntimeConfigSource<F> where F: Factor for every factor in the RuntimeFactors collection. This works out that the runtime embedder then can implement FactorRuntimeConfigSource<F> for each of the factors they use.

I recommend checking out the tests and the smoke test for how this works in practice.