Another awkward hold-over from the SGX/ringbuffer days. We have a host::CCHostConfig type, that is directly JSON-serialisable - this is what the operators give us. We convert that to a near-identical-bar-some-naming-and-instantiation type called ccf::StartupConfig. One thing that used to do was strip out the host-only bits so the enclave didn't worry about them, but we want to push much of that reasoning into the "enclave" code. It also did some early validation/reification, but we think that can all be pushed to time-of-use, removing some TOCTOU concerns.