Add maven-javadoc-plugin and maven-source-plugin to storage-targets/cds-feature-attachments-oss

Try to fix the failing maven deployment https://github.com/cap-java/cds-feature-attachments/actions/runs/17241063009/job/48918884538
with this, because the error is:

Deployment failed
pkg:maven/com.sap.cds/[email protected]:
- Sources must be provided but not found in entries
- Javadocs must be provided but not found in entries

Author: lisajulia

storage-targets/cds-feature-attachments-oss/pom.xml

@@ -169,6 +169,32 @@
                 </configuration>
             </plugin>
 
+            <plugin>
+                <artifactId>maven-javadoc-plugin</artifactId>
+                <configuration>
+                    <failOnError>true</failOnError>
+                    <doclint>all,-missing</doclint>
+                </configuration>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>jar</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+
+            <plugin>
+                <artifactId>maven-source-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <goals>
+                            <goal>jar</goal>
+                        </goals>
+                    </execution>
+                </executions>
+            </plugin>
+
         </plugins>
     </build>
     <profiles>