feat: reusable build-and-push and deploy-restart composite actions

- build-and-push: multi-arch Docker build via remote Buildx builder over SSH
- deploy-restart: kubectl rollout restart with kubeconfig validation
- README with usage examples and required secrets

deploy-restart/action.yaml

@@ -0,0 +1,67 @@
+name: Deploy Restart (kubectl rollout)
+description: Validate KUBE_CONFIG, install kubectl, and perform a rollout restart of a Kubernetes deployment.
+
+inputs:
+  kube_config:
+    description: Full kubeconfig YAML content (pass via secrets)
+    required: true
+  deployment_name:
+    description: Name of the Kubernetes Deployment to restart
+    required: true
+  namespace:
+    description: Kubernetes namespace of the deployment
+    required: false
+    default: default
+  kube_version:
+    description: Kubernetes version to download (stable, or a specific version like v1.31.0)
+    required: false
+    default: stable
+
+runs:
+  using: composite
+  steps:
+    - name: Check KUBE_CONFIG validity
+      shell: bash
+      env:
+        KUBE_CONFIG: ${{ inputs.kube_config }}
+      run: |
+        if [ -z "${KUBE_CONFIG}" ] || [ "${KUBE_CONFIG}" = "" ] || [ "${KUBE_CONFIG// }" = "" ]; then
+          echo "KUBE_CONFIG is not set or is empty."
+          exit 1
+        fi
+
+    - name: Check out repository
+      uses: actions/checkout@v4
+
+    - name: Download and install kubectl
+      shell: bash
+      env:
+        KUBE_VERSION: ${{ inputs.kube_version }}
+      run: |
+        apt-get update -y
+        apt-get install -y curl
+        if [ "${KUBE_VERSION}" = "stable" ]; then
+          KUBE_VER="$(curl -L -s https://dl.k8s.io/release/stable.txt)"
+        else
+          KUBE_VER="${KUBE_VERSION}"
+        fi
+        curl -LO "https://dl.k8s.io/release/${KUBE_VER}/bin/linux/amd64/kubectl"
+        install -m 0755 kubectl /usr/local/bin/kubectl
+        kubectl version --client
+
+    - name: Set up kubeconfig
+      shell: bash
+      env:
+        KUBE_CONFIG: ${{ inputs.kube_config }}
+      run: |
+        echo "${KUBE_CONFIG}" > kubeconfig.yaml
+        kubectl --kubeconfig=kubeconfig.yaml cluster-info
+
+    - name: Rollout restart
+      shell: bash
+      env:
+        DEPLOYMENT_NAME: ${{ inputs.deployment_name }}
+        NAMESPACE: ${{ inputs.namespace }}
+      run: |
+        kubectl --kubeconfig=kubeconfig.yaml rollout restart \
+          deployment "${DEPLOYMENT_NAME}" -n "${NAMESPACE}"