Assigns the appropriate key usage for a given set of keys based on the current topology request and necessary authorizations. In most cases, the request is expected to be signed with Namespace keys. However, for requests like OwnerToKeyMapping or PartyToKeyMapping, keys must be able to prove their ownership. For these requests we also accept namespace as a valid usage when verifying a signature, as this ensures backwards compatibility (e.g. older topology states might have mistakenly added a namespace key to this mapping). By enforcing only ProofOfOwnership on the sign path, we ensure that this new restriction applies to any newly added key, preventing the addition of namespace-only keys to these requests.