Add client-hadoop3 module

the new client/hdfs3 and shaded/client-hadoop3 modules are currently a
copy of the existing client/hdfs and shaded/client modules

the addition of this will allow for changes that are available only in
hadoop3, such as
Alluxio#16017 (comment)

both client jars will be built by default, but the symlink at
client/alluxio-VERSION-client.jar will point to the hadoop-2 one to
maintain backcompat. if the hadoop-3 profile is activated by adding
`-Phadoop-3`, then the symlink will be overridden to point to the new
hadoop3 shaded client jar

pr-link: Alluxio#16699
change-id: cid-a6ffd09414e8259078fd5a8f68c3e287d85feec5

core/client/hdfs3/pom.xml

@@ -0,0 +1,57 @@
+<!--
+
+    The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
+    (the "License"). You may not use this work except in compliance with the License, which is
+    available at www.apache.org/licenses/LICENSE-2.0
+
+    This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
+    either express or implied, as more fully set forth in the License.
+
+    See the NOTICE file distributed with this work for information regarding copyright ownership.
+
+-->
+<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+  <parent>
+    <groupId>org.alluxio</groupId>
+    <artifactId>alluxio-core-client</artifactId>
+    <version>2.10.0-SNAPSHOT</version>
+  </parent>
+  <artifactId>alluxio-core-client-hdfs3</artifactId>
+  <packaging>jar</packaging>
+  <name>Alluxio Core - Client - HDFS3</name>
+  <description>HDFS Client of Alluxio Core For HDFS 3</description>
+
+  <properties>
+    <!-- The following paths need to be defined here as well as in the parent pom so that mvn can -->
+    <!-- run properly from sub-project directories -->
+    <build.path>${project.parent.parent.parent.basedir}/build</build.path>
+    <failIfNoTests>false</failIfNoTests>
+  </properties>
+
+  <dependencies>
+    <!-- Internal dependencies -->
+    <dependency>
+      <groupId>org.alluxio</groupId>
+      <artifactId>alluxio-core-client-hdfs</artifactId>
+      <version>${project.version}</version>
+    </dependency>
+  </dependencies>
+
+  <build>
+    <plugins>
+      <!-- Export test classes in a test-jar so that other projects can use them for testing -->
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <executions>
+          <execution>
+            <goals>
+              <goal>test-jar</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
+    </plugins>
+  </build>
+</project>

core/client/pom.xml

@@ -25,6 +25,7 @@
   <modules>
     <module>fs</module>
     <module>hdfs</module>
+    <module>hdfs3</module>
   </modules>
 
   <properties>