feat: enhance ci with test matrix

[zhaque44]

Adding test matrix for different OS:

Updating to follow CI best practices:

• Use actions/cache to cache Go build/test dependencies across OSes for faster builds.
• Parallelize jobs to run build-test and unit-test concurrently.
• Set fail-fast: false in the matrix strategy to continue running tests even if one environment fails.

[mumoshu]

Our go-test does not depend on a working Kubernetes cluster.

So we might split this unit-test into two, unit-test and probably e2e-test:

• unit-test should not depend on K8s, and simply setting up Go, go cache, and running go test ./... (via make) should do the job.
• e2e-test should run the e2e tests written in shellscript, which depends on a working Kubernetes cluster.

This way, we won't need a lot of if: ${{ matrix.os == 'ubuntu-latest' }}, because:

• unit-test should run all the steps against all the supported oses.
• e2e-test should run all the steps against all the supported oses. (Not sure if kind is able to run on all the managed GHA runners, especially macos and windows, but that's the idea.)

WDYT?

[zhaque44]

that sounds like an idea that can work: One question I have here is, which tests? are unit and which are e2e they are not listed from what it seems