auto-select by detecting runtimes.

RunConfig describes the runtime config parameters for container instances (aka Config in other libraries) Fields (ordered according to spec): Memory, MemorySwap, CpuShares aren't necessary * https://github.com/opencontainers/image-spec/blob/main/config.md#properties (Config field) * https://github.com/moby/moby/blob/master/api/types/container/config.go#L70 Note: related to pkg/docker/dockerimage/ContainerConfig TODO: refactor into one set of common structs later.