docs(sample): add native-image sample (#621)

Relocating the sample from native-image-support to this repository

`mvn clean verify -DskipTests -P lint` passes.

Fixes #<issue_number_goes_here> ☕️

If you write sample code, please follow the [samples format](
https://github.com/GoogleCloudPlatform/java-docs-samples/blob/main/SAMPLE_FORMAT.md).

Author: suztomo

tasks/pom.xml

@@ -31,6 +31,7 @@
     <module>install-without-bom</module>
     <module>snapshot</module>
     <module>snippets</module>
+    <module>native-image-sample</module>
   </modules>
 
   <build>