packages vmtest steps into libbpf/ci actions

[chantra]

We have some steps/actions in kernel-patches/vmtest that are not fully encapsulated:

.github/actions/veristat_baseline_compare/action.yml:      run: ./.github/scripts/compare-veristat-results.sh
.github/scripts/compare-veristat-results.sh:python3 ./.github/scripts/veristat_compare.py compare.csv
.github/scripts/tar-artifact.sh:    "scripts/"
.github/workflows/kernel-build.yml:          bash .github/scripts/get-commit-metadata.sh
.github/workflows/kernel-build.yml:          bash .github/scripts/prepare-incremental-builds.sh ${{ steps.get-commit-metadata.outputs.commit }}
.github/workflows/kernel-build.yml:          bash .github/scripts/tar-artifact.sh ${{ inputs.arch }} ${{ inputs.toolchain_full }}

Because the actions/workflow use local copies of the scripts, they can only be used by the kernel-patches/vmtest (or anything that copies the files locally). Running this from another repo would fail to find those scripts.

We should package those individual steps into libbpf/ci actions which we then can re-use from kernel-patches/vmtest and/or libbpf/libbpf.

[chantra]

hint.

As part of #141 a bunch of the logic got copied into libbpf/ci already:

.github/scripts/tar-artifact.sh:    "scripts/"
.github/workflows/kernel-build.yml:          bash .github/scripts/get-commit-metadata.sh
.github/workflows/kernel-build.yml:          bash .github/scripts/prepare-incremental-builds.sh ${{ steps.get-commit-metadata.outputs.commit }}
.github/workflows/kernel-build.yml:          bash .github/scripts/tar-artifact.sh ${{ inputs.arch }} ${{ inputs.toolchain_full }} 1

so what we need to do here is to convert those steps into actions, and then change vmtests to use those.

Feel free to cut individual issues/PR for each of those actions.