CI: Build cache cpp-sdk-build contains unnecessary archives

[aLekSer]

Currently the following files are added to build cache for every new build:

agonessdk-1.0.0-b8432d1-linux-arch_64.tar.gz

What happened:

What you expected to happen:

The moment it happened is here:

agones/sdks/cpp/Makefile

Line 38 in 88f1d4e

cd $(package_path) && tar cf $(build_path)/agonessdk-$(VERSION)-linux-arch_64.tar.gz *

I expect that package_path (.install) would be used to store all the archives. And .build would contain only files needed for the build.

How to reproduce it (as minimally and precisely as possible):
du -sh ./sdks/cpp/.build
make archive
du -sh ./sdks/cpp/.build - becomes significantly bigger but should not.

Anything else we need to know?:

Environment:

• Agones version:
• Kubernetes version (use kubectl version):
• Cloud provider or hardware configuration:
• Install method (yaml/helm):
• Troubleshooting guide log(s):
• Others:

[markmandel]

This is why the cpp build cache is 6+ GB at the moment.

Worth noting, changing this position of these artifacts will affect the cloudbuild.yaml and also the do-release target (and maybe some others) so it's worth a review to see what can be found.