@Override
    public TopicFetcher getFetcher(String fetchKey) {
        return fetchers.get(fetchKey);
    }
create fetcher (pulsar,tube,kafka)

@param topic {@link InLongTopic}
@return {@link TopicFetcher}
inlong-sdk/sort-sdk/src/main/java/org/apache/inlong/sdk/sort/manager/InlongSingleTopicManager.java