Put TF Java version information in published POM files.

Version information can be retrieved with

```
org.tensorflow.TensorFlow.class.getPackage().getImplementationVersion()
```

For TensorFlow 1.14.0, for example, this would return the string
"1.14.0".

This version string reflects the TF Java API version, not necessarily
the underlying TensorFlow runtime version that may be retrieved via
org.tensorflow.TensorFlow.version().

PiperOrigin-RevId: 260584561

tensorflow/java/maven/pom.xml

@@ -90,6 +90,17 @@
           </execution>
         </executions>
       </plugin>
+      <plugin>
+        <groupId>org.apache.maven.plugins</groupId>
+        <artifactId>maven-jar-plugin</artifactId>
+        <configuration>
+          <archive>
+            <manifest>
+              <addDefaultImplementationEntries>true</addDefaultImplementationEntries>
+            </manifest>
+          </archive>
+        </configuration>
+      </plugin>
     </plugins>
   </build>