public ApplicationFile getApplicationFile(Path relativePath, LocalSession.Mode mode) {
        if (mode.equals(Session.Mode.WRITE)) {
            markSessionEdited();
        }
        return getApplicationPackage().getFile(relativePath);
    }
Returns application id read from ZooKeeper. Will return Optional.empty() if not found
configserver/src/main/java/com/yahoo/vespa/config/server/session/Session.java