Add an experimental GitHub Actions workflow for CI

All the credits goes to @itscaro's work at https://github.com/roboll/helmfile/pull/2084. The only change I made is related to the main branch rename.

.github/workflows/ci.yaml

@@ -0,0 +1,98 @@
+name: Go
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v2
+    - name: Cache libraries
+      uses: actions/cache@v2
+      env:
+        cache-name: cache-go
+      with:
+        path: ~/go/pkg/mod
+        key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-build-${{ env.cache-name }}-
+          ${{ runner.os }}-build-
+          ${{ runner.os }}-
+    - name: Set up Go
+      uses: actions/setup-go@v2
+      with:
+        go-version: 1.17
+    - name: Env
+      run: go env
+    - name: Build
+      run: make build build-test-tools
+    - name: Test
+      run: make check pristine test
+
+    - name: Prepare tar to upload built binaries
+      run: tar -cvf built-binaries.tar helmfile diff-yamls yamldiff
+    - name: Upload built binaries
+      uses: actions/upload-artifact@v2
+      with:
+        name: built-binaries-${{ github.run_id }}
+        path: built-binaries.tar
+        retention-days: 1
+    - name: Display built binaries
+      run: ls -l helmfile diff-yamls yamldiff
+
+  integration_tests:
+    needs: tests
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+       include:
+         - helm-version: v3.4.2
+         - helm-version: v3.5.4
+         - helm-version: v3.6.3
+         - helm-version: v3.7.2
+         - helm-version: v3.8.0
+    steps:
+    - uses: actions/checkout@v2
+    - name: Cache libraries
+      uses: actions/cache@v2
+      env:
+        cache-name: cache-go
+      with:
+        path: ~/go/pkg/mod
+        key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/go.sum') }}
+        restore-keys: |
+          ${{ runner.os }}-build-${{ env.cache-name }}-
+          ${{ runner.os }}-build-
+          ${{ runner.os }}-
+    - name: Set up Go
+      uses: actions/setup-go@v2
+      with:
+        go-version: 1.17
+    - name: Env
+      run: go env
+
+    - name: Download built binaries
+      uses: actions/download-artifact@v2
+      with:
+        name: built-binaries-${{ github.run_id }}
+    - name: Extract tar to get built binaries
+      run: tar -xvf built-binaries.tar
+    - name: Display built binaries
+      run: ls -l helmfile diff-yamls yamldiff
+
+    - name: Install test dependencies
+      env:
+        HELM_VERSION: ${{ matrix.helm-version }}
+      run: make -C .circleci helm vault sops kustomize
+    - name: Start minikube
+      uses: medyagh/setup-minikube@master
+    - name: Execute integration tests
+      env:
+        HELMFILE_HELM3: 1
+        TERM: xterm
+      run: make integration