Add protocol dto classes #5

- partial coordinator API

src/main/java/com/github/nginate/kafka/protocol/messages/request/GroupCoordinatorRequest.java

@@ -0,0 +1,23 @@
+package com.github.nginate.kafka.protocol.messages.request;
+
+import com.github.nginate.kafka.protocol.messages.Request;
+import com.github.nginate.kafka.protocol.types.Type;
+import lombok.Builder;
+import lombok.Data;
+import lombok.EqualsAndHashCode;
+
+import static com.github.nginate.kafka.protocol.types.TypeName.STRING;
+
+/**
+ * The offsets for a given consumer group are maintained by a specific broker called the group coordinator. i.e., a
+ * consumer needs to issue its offset commit and fetch requests to this specific broker. It can discover the current
+ * coordinator by issuing a group coordinator request.
+ */
+@Data
+@Builder
+//@ApiKey(ApiKeys.) FIXME
+@EqualsAndHashCode(callSuper = true)
+public class GroupCoordinatorRequest extends Request {
+    @Type(STRING)
+    private String groupId;
+}

src/main/java/com/github/nginate/kafka/protocol/messages/response/GroupCoordinatorResponse.java

@@ -0,0 +1,24 @@
+package com.github.nginate.kafka.protocol.messages.response;
+
+import com.github.nginate.kafka.protocol.messages.Response;
+import com.github.nginate.kafka.protocol.types.Type;
+import lombok.Data;
+import lombok.EqualsAndHashCode;
+
+import static com.github.nginate.kafka.protocol.types.TypeName.INT16;
+import static com.github.nginate.kafka.protocol.types.TypeName.INT32;
+import static com.github.nginate.kafka.protocol.types.TypeName.STRING;
+
+@Data
+//@ApiKey(ApiKeys.) FIXME
+@EqualsAndHashCode(callSuper = true)
+public class GroupCoordinatorResponse extends Response {
+    @Type(INT16)
+    private Short errorCode;
+    @Type(INT32)
+    private Integer coordinatorId;
+    @Type(STRING)
+    private String coordinatorHost;
+    @Type(INT32)
+    private Integer coordinatorPort;
+}