[BEAM-5328] Starter Archetype generation fix & correctness test

[Mikhail-Ivanov]

Fixed archetype-starter build script and provided an appropriate unit tests in accordance with: BEAM-5328

Post-Commit Tests Status (on master branch)

Lang	SDK	Apex	Dataflow	Flink	Gearpump	Samza	Spark
Go		---	---	---	---	---	---
Java
Python		---			---	---	---

[lukecwik]

To finish BEAM-5328, you also want to ensure that your test runs via Jenkins similar to how the quickstart tests are currently running. To do this you'll need to:

1. make a task which is capable of executing this StarterArchetype like:
   

   beam/buildSrc/src/main/groovy/org/apache/beam/gradle/BeamModulePlugin.groovy

   Line 1294 in a2b0ad1

   project.ext.createJavaExamplesArchetypeValidationTask = {

2. add your task to the runJavaExamplesValidationTask:

   beam/release/build.gradle

   Line 30 in a2b0ad1

   task runJavaExamplesValidationTask {

(optional) As another follow-up, it would be nice to rename runJavaExamplesValidationTask to not be "examples" specific but something like runJavaPostReleaseTests. Might want to get an opinion from @alanmyrvold as to the name.

I'll merge this as is once the tests are green and allow you to open up follow-up PRs.

[lukecwik]

retest this please