Configure maven-source-plugin execution in parent POM

This ensures all modules will have source jars built

Change-Id: I11a762f54cc8b059eff3bd99138a7efa9723b19f
Signed-off-by: Matthias Sohn <matthias.sohn@sap.com>

pom.xml

@@ -377,6 +377,20 @@
           </execution>
         </executions>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-source-plugin</artifactId>
+        <inherited>true</inherited>
+        <executions>
+          <execution>
+            <id>attach-sources</id>
+            <phase>process-classes</phase>
+            <goals>
+              <goal>jar</goal>
+            </goals>
+          </execution>
+        </executions>
+      </plugin>
     </plugins>
   </build>