showcase samples should be part of golden tests

[zhumin8]

sample snippets here should be part of the golden testing for Showcase.

Steps to identify this:

rm -rf showcase/gapic-showcase/samples/
mvn clean install -DskipTests
cd showcase

then mvn compile -P update, expect the samples should be re-generated and added back.
But this samples folder is not re-generated

[blakeli0]

I think it worked before, could it be an issue caused by migrating Showcase to the hermetic build scrips? cc: @diegomarquezp @JoeWang1127

[JoeWang1127]

Probably because we didn't copy sample directory in https://github.com/googleapis/sdk-platform-java/blob/main/showcase/scripts/generate_components.sh

[lqiu96]

Keeping this a P2 issue. Seems to be due to a regression in the hermetic build scripts.

[blakeli0]

This was done in the early phase of hermetic build when we didn't have the image. We should migrate the showcase module to use hermetic build image now, with a dedicated generation_config.yaml.