Add melange/apko build pipeline and Kubernetes manifests

- Add melange.yaml for distroless package build
- Add apko.yaml for minimal container image
- Add GitHub Actions workflow for melange/apko CI build
- Add Kubernetes manifests (deployment, service, configmap, secret, redis)
- Update Dockerfile, .gitignore, and docker-compose.yml

k8s/redis-statefulset.yaml

@@ -0,0 +1,72 @@
+apiVersion: apps/v1
+kind: StatefulSet
+metadata:
+  name: redis
+  namespace: apcupsd
+  labels:
+    app.kubernetes.io/name: redis
+    app.kubernetes.io/part-of: apcupsd-client
+spec:
+  serviceName: redis
+  replicas: 1
+  selector:
+    matchLabels:
+      app.kubernetes.io/name: redis
+  template:
+    metadata:
+      labels:
+        app.kubernetes.io/name: redis
+    spec:
+      securityContext:
+        runAsUser: 999
+        runAsGroup: 999
+        fsGroup: 999
+      containers:
+        - name: redis
+          image: redis:7-alpine
+          command:
+            - redis-server
+            - --appendonly
+            - "yes"
+            - --appendfsync
+            - everysec
+          ports:
+            - containerPort: 6379
+              protocol: TCP
+          livenessProbe:
+            exec:
+              command:
+                - redis-cli
+                - ping
+            initialDelaySeconds: 10
+            periodSeconds: 10
+            timeoutSeconds: 3
+            failureThreshold: 5
+          readinessProbe:
+            exec:
+              command:
+                - redis-cli
+                - ping
+            initialDelaySeconds: 5
+            periodSeconds: 5
+            timeoutSeconds: 3
+            failureThreshold: 3
+          resources:
+            requests:
+              memory: "64Mi"
+              cpu: "50m"
+            limits:
+              memory: "128Mi"
+              cpu: "250m"
+          volumeMounts:
+            - name: redis-data
+              mountPath: /data
+  volumeClaimTemplates:
+    - metadata:
+        name: redis-data
+      spec:
+        accessModes:
+          - ReadWriteOnce
+        resources:
+          requests:
+            storage: 1Gi