Refactor GitHub workflows for reusability

Separate the k0s and airgap image bundle builds into their own reusable
workflows, enhancing composability and enabling reuse in higher-level
workflows.

The new reusable workflows are parameterized over os and arch. Hopefully
they can be reused by the ARM builds at some point as well.

To increase the reusability and generalization of the k0s build
workflow, extract the airgap image bundle build into a separate
reusable workflow. Additionally, eliminate the special case for the
smoke test matrix generation. Instead, introduce a dedicated "Prepare"
workflow that generates the matrix for the regular and Autopilot smoke
tests.

Signed-off-by: Tom Wieczorek <twieczorek@mirantis.com>

.github/workflows/build-airgap-image-bundle.yml

@@ -0,0 +1,66 @@
+name: "Build :: Airgap image bundle"
+
+on:
+  workflow_call:
+    inputs:
+      target-os:
+        type: string
+        description: The OS to build the airgap image bundle for.
+      target-arch:
+        type: string
+        required: true
+        description: The architecture to build the airgap image bundle for.
+    outputs:
+      cache-key:
+        description: The airgap image bundle's cache key.
+        value: ${{ jobs.build.outputs.cache-key }}
+
+jobs:
+  build:
+    name: "${{ inputs.target-os }}-${{ inputs.target-arch }}"
+    runs-on: ubuntu-22.04
+
+    outputs:
+      cache-key: ${{ steps.cache-airgap-image-bundle-calc-key.outputs.cache-key }}
+
+    env:
+      TARGET_OS: ${{ inputs.target-os }}
+      TARGET_ARCH: ${{ inputs.target-arch }}
+
+    steps:
+      - name: "Build :: Checkout"
+        uses: actions/checkout@v3
+        with:
+          persist-credentials: false
+
+      - name: "Download :: Airgap image list"
+        uses: actions/download-artifact@v3
+        with:
+          name: airgap-image-list-${{ inputs.target-os }}-${{ inputs.target-arch }}
+
+        # Capture the calculated image bundle source hash in a build output, so
+        # it can be shared between the cache actions in this job and in the
+        # smoketests. Do this in a separate step, as the hashFiles function is
+        # evaluated before the step execution. So all the required files need to
+        # exist before that.
+      - name: "Cache :: Airgap image bundle :: Calculate cache key"
+        id: cache-airgap-image-bundle-calc-key
+        env:
+          HASH_VALUE: ${{ hashFiles('Makefile', 'airgap-images.txt', 'hack/image-bundler/*') }}
+        run: |
+          printf 'cache-key=build-airgap-image-bundle-%s-%s-%s\n' "$TARGET_OS" "$TARGET_ARCH" "$HASH_VALUE" >> "$GITHUB_OUTPUT"
+
+      - name: "Cache :: Airgap image bundle"
+        id: cache-airgap-image-bundle
+        uses: actions/cache@v3
+        with:
+          key: ${{ steps.cache-airgap-image-bundle-calc-key.outputs.cache-key }}
+          path: airgap-image-bundle-${{ inputs.target-os }}-${{ inputs.target-arch }}.tar
+          lookup-only: true
+
+      - name: "Build :: Airgap image bundle"
+        if: steps.cache-airgap-image-bundle.outputs.cache-hit != 'true'
+        run: |
+          mkdir -p "embedded-bins/staging/$TARGET_OS/bin"
+          make --touch airgap-images.txt
+          make "airgap-image-bundle-$TARGET_OS-$TARGET_ARCH.tar"

.github/workflows/build-k0s.yml

@@ -0,0 +1,92 @@
+name: "Build :: k0s"
+
+on:
+  workflow_call:
+    inputs:
+      target-os:
+        type: string
+        required: true
+        description: The OS to build k0s for (linux or windows).
+      target-arch:
+        type: string
+        required: true
+        description: The architecture to build k0s for.
+
+jobs:
+  build:
+    name: ${{ inputs.target-os }}-${{ inputs.target-arch }}
+    runs-on: ubuntu-22.04
+
+    env:
+      TARGET_OS: ${{ inputs.target-os }}
+      TARGET_ARCH: ${{ inputs.target-arch }}
+
+    steps:
+      - name: "Build :: Checkout"
+        uses: actions/checkout@v3
+        with:
+          fetch-depth: 0 # for `git describe`
+          persist-credentials: false
+
+      - name: "Build :: Prepare"
+        id: build-prepare
+        run: |
+          .github/workflows/prepare-build-env.sh
+
+          executableSuffix=''
+          if [ "TARGET_OS" = windows ]; then
+            executableSuffix=.exe
+          fi
+          echo executable-suffix="$executableSuffix" >>"$GITHUB_OUTPUT"
+
+      - name: "Cache :: embedded binaries"
+        uses: actions/cache@v3
+        with:
+          key: build-k0s-${{ inputs.target-os }}-${{ inputs.target-arch }}-embedded-bins-${{ hashFiles('embedded-bins/**/*') }}
+          path: |
+            .bins.${{ inputs.target-os }}.stamp
+            bindata_${{ inputs.target-os }}
+            embedded-bins/staging/${{ inputs.target-os }}/bin/
+            embedded-bins/Makefile.variables
+            pkg/assets/zz_generated_offsets_${{ inputs.target-os }}.go
+
+      - name: "Cache :: GOCACHE"
+        uses: actions/cache@v3
+        with:
+          key: build-k0s-${{ inputs.target-os }}-${{ inputs.target-arch }}-gocache-${{ github.ref_name }}-${{ github.sha }}
+          restore-keys: |
+            build-k0s-${{ inputs.target-os }}-${{ inputs.target-arch }}-gocache-${{ github.ref_name }}-
+          path: |
+            build/cache/go/build
+
+      - name: "Cache :: GOMODCACHE"
+        uses: actions/cache@v3
+        with:
+          key: build-k0s-${{ inputs.target-os }}-${{ inputs.target-arch }}-gomodcache-${{ hashFiles('go.sum') }}
+          path: |
+            build/cache/go/mod
+
+      - name: "Build :: k0s"
+        run: |
+          make bindata
+          make --touch codegen
+          make build
+
+      - name: "Upload :: k0s"
+        uses: actions/upload-artifact@v3
+        with:
+          name: k0s-${{ inputs.target-os }}-${{ inputs.target-arch }}
+          path: |
+            k0s${{ steps.build-prepare.outputs.executable-suffix }}
+            k0s${{ steps.build-prepare.outputs.executable-suffix }}[.]exe
+
+      - name: "Build :: Airgap image list"
+        if: inputs.target-os != 'windows'
+        run: make airgap-images.txt && cat airgap-images.txt
+
+      - name: "Upload :: Airgap image list"
+        if: inputs.target-os != 'windows'
+        uses: actions/upload-artifact@v3
+        with:
+          name: airgap-image-list-${{ inputs.target-os }}-${{ inputs.target-arch }}
+          path: airgap-images.txt