Packaging: Add commons codec jar to packaged zip

In order to use the `esusers` tool and to crypt passwords, one needs
to have the jar packaged in the zip release. This adds the depdendency
to the assembly descriptor.

Original commit: elastic/x-pack-elasticsearch@82ae451892

src/main/assemblies/plugin.xml

@@ -25,5 +25,13 @@
                 <exclude>org.elasticsearch:elasticsearch</exclude>
             </excludes>
         </dependencySet>
+        <dependencySet>
+            <outputDirectory>/</outputDirectory>
+            <useProjectArtifact>true</useProjectArtifact>
+            <useTransitiveFiltering>true</useTransitiveFiltering>
+            <includes>
+                <include>commons-codec:commons-codec</include>
+            </includes>
+        </dependencySet>
     </dependencySets>
 </assembly>