code: public boolean addSubsystemFileSourceFromZipFile(String subsystem, File file) throws IOException {
          try (ZipFile zip = new ZipFile(file)) {
              String entryName = "subsystem-templates/"+subsystem;
              ZipEntry entry = zip.getEntry(entryName);
              if (entry != null) {
                  addSubsystemFileSource(subsystem, file, entry);
                  return true;
              }
          }
          return false;
      }
docs: Adds the file source for the specified subsystem, from the specified zip file.
  @param subsystem
  @param file
  @return true if such subsystem file source was found and added; false otherwise
  @throws IOException