SONAR-1792: Generate a help mojo which describes all mojos in a sonar-dev-maven-plugin

subprojects/sonar-dev-maven-plugin/pom.xml

@@ -289,6 +289,19 @@
           </execution>
         </executions>
       </plugin>
+
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-plugin-plugin</artifactId>
+        <executions>
+          <execution>
+            <id>help-mojo</id>
+            <goals>
+              <goal>helpmojo</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>