@Nullable
  Long getContainerHealthTimeout() {
    return config.Healthcheck == null ? null : config.Healthcheck.Timeout;
  }
Returns the operating system for which this container was built. See the <a
href="https://github.com/opencontainers/image-spec/blob/master/config.md#properties">OCI Image
Configuration specification</a> for acceptable values.

@return the {@code os} field
jib-core/src/main/java/com/google/cloud/tools/jib/image/json/ContainerConfigurationTemplate.java