@Override
    public Set<String> getManagedInLongTopics() {
        return new HashSet<>(fetchers.keySet());
    }
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