public Container searcher(String id, String chainName, Class<? extends Searcher> searcher, ConfigInstance... configs) {
                List<ComponentItem<? extends Searcher>> chain = searchers.get(chainName);
                if (chain == null) {
                    chain = new ArrayList<>();
                    searchers.put(chainName, chain);
                }
                chain.add(new ComponentItem<>(id, searcher, configs));
                return this;
            }
@param id        component id
@param chainName chain name to add searcher
@param searcher  add this searcher to the search chain
@param configs   local searcher configs
@return builder
application/src/main/java/com/yahoo/application/Application.java