Add Sevntu-checkstyle diamond operator check

etc/checkstyle.xml

@@ -107,5 +107,8 @@ under the License.
          <property name="severity" value="ignore"/>
       </module>
 
+      <!-- Sevntu checks, http://sevntu-checkstyle.github.io/sevntu.checkstyle/ -->
+      <module name="DiamondOperatorForVariableDefinition"/>
+
    </module>
 </module>

pom.xml

@@ -1062,6 +1062,11 @@
             <artifactId>maven-checkstyle-plugin</artifactId>
             <version>2.17</version>
             <dependencies>
+               <dependency>
+                  <groupId>com.github.sevntu.checkstyle</groupId>
+                  <artifactId>sevntu-checkstyle-maven-plugin</artifactId>
+                  <version>1.21.0</version>
+               </dependency>
                <!-- This was initially done to enforce name on Parameter annotation
                     I've developed a customized check and I needed this jar to deploy the specialized checkstyle -->
                <dependency>
@@ -1228,4 +1233,13 @@
          </plugin>
       </plugins>
    </reporting>
+
+   <pluginRepositories>
+      <pluginRepository>
+          <id>sevntu-maven</id>
+          <name>sevntu-maven</name>
+          <url>http://sevntu-checkstyle.github.io/sevntu.checkstyle/maven2</url>
+      </pluginRepository>
+   </pluginRepositories>
+
 </project>