### Motivation:
In the coming weeks, we want to restructure the LambdaRuntime internals in such a way, that we allocate a lot less resources per invocation. To accomplish this, we want to encode and decode the ControlPlaneAPI requests directly from their semantic value. For this reason, we need a specialized ControlPlaneRequest and ControlPlaneResponse type that we can encode from and decode into.
### Modifications:
- Add `ControlPlaneRequest`, `ControlPlaneResponse`
- Move `Invocation` and `ErrorResponse` into same file as `ControlPlaneRequest`
- Remove `Lambda` namespace around `Invocation`