Fixes#8755
Since I was updating the interface, i also added the missing `GetNamespace()`.
Depending upon how you look at it, this is a breaking change since it adds methods to the exported interface `api.ConfigEntry`. Given that you cannot define your own config entry kinds, and all of the machinery of the `api.Client` acts like a factory to construct the canned ones from the rest of the module, this feels like it's not a problematic change as it would only break someone who had reimplemented the `ConfigEntry` interface themselves for no apparent utility?
In addition to exposing compilation over the API cleaned up the structures that would be exchanged to be cleaner and easier to support and understand.
Also removed ability to configure the envoy OverprovisioningFactor.