chore(store): add some simple docst

Signed-off-by: daniel-y <[email protected]>

store/src/main/java/com/automq/rocketmq/store/StreamStore.java

@@ -22,8 +22,25 @@
 import com.automq.rocketmq.stream.api.RecordBatch;
 import java.util.concurrent.CompletableFuture;
 
+/**
+ * A high level abstraction of stream store, hidden the details of S3Stream module.
+ */
 public interface StreamStore {
+    /**
+     * Fetch records from stream store.
+     *
+     * @param streamId the target stream id.
+     * @param startOffset the start offset of the fetch.
+     * @param maxCount the max return count of the fetch.
+     * @return the future of fetch result.
+     */
     CompletableFuture<FetchResult> fetch(long streamId, long startOffset, int maxCount);
 
+    /**
+     * Append record batch to stream store.
+     * @param streamId the target stream id.
+     * @param recordBatch the record batch to append.
+     * @return the future of append result.
+     */
     CompletableFuture<AppendResult> append(long streamId, RecordBatch recordBatch);
 }