Add CI stage to assemble a JAR file of sample with dependencies

- Let's assemble a JAR file of the sample with the Maven "package"
  command, so that is easily run in CI. In order to build a JAR
  with the dependencies, we had to utilize the maven-assembly-plugin
  in the pom.xml and set the mainClass property in the configuration
  section of the plugin.

.github/workflows/test-kotlin-samples.yml

@@ -29,3 +29,6 @@ jobs:
             - name: Unpack APDFL from Maven Central
               working-directory: ${{ matrix.dir }}
               run: mvn -e process-resources
+            - name: Compile and assemble sample JAR file with dependencies
+              working-directory: ${{ matrix.dir }}
+              run: mvn -e package

TextExtract/pom.xml

@@ -194,6 +194,28 @@
                     </execution>
                 </executions>
             </plugin>
+            <plugin>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <phase>package</phase>
+                        <goals>
+                            <goal>single</goal>
+                        </goals>
+                    </execution>
+                </executions>
+                <configuration>
+                    <archive>
+                        <manifest>
+                            <addClasspath>true</addClasspath>
+                            <mainClass>com.datalogics.pdfl.samples.TextExtractKt</mainClass>
+                        </manifest>
+                    </archive>
+                    <descriptorRefs>
+                        <descriptorRef>jar-with-dependencies</descriptorRef>
+                    </descriptorRefs>
+                </configuration>
+            </plugin>
         </plugins>
         <pluginManagement>
             <plugins>