Add dev/stg/prod environments with per-env values, configmaps and secrets

- Move env-specific config into environments/<env>/{values,configmap,secret}.yaml
  for both nginx-chart and mysql-chart (dev, stg, prod)
- Make templates env-agnostic: resource names come from values
  (configMap.name, secret.name)
- nginx deployment mounts env ConfigMap and loads env Secret via envFrom
- mysql statefulset reads DB config from ConfigMap, passwords from Secret
- Remove mysql-chart/templates/secret.yaml (secrets are now per-env manifests)
- Add README with layout and deploy commands

nginx-chart/values.yaml

@@ -1,13 +1,38 @@
+# Base (default) values for nginx-chart.
+#
+# Environment-specific overrides live in environments/<env>/values.yaml and are
+# merged on top of this file at deploy time:
+#
+#   helm upgrade --install nginx ./nginx-chart -n <namespace> --create-namespace \
+#     -f nginx-chart/environments/<env>/values.yaml
+#
+# Available environments: dev, stg, prod
+
 replicaCount: 1
-namespace: "dev"
+
+namespace: dev
+
 image:
   repository: imageregistry.gen-itech.com/demo/applicationtest
   tag: "39"
   pullPolicy: IfNotPresent
+
+# Name of the docker-registry pull secret (created by environments/<env>/secret.yaml)
+imagePullSecrets: harbor-secret
+
 service:
   type: ClusterIP
   port: 80
+
 ingress:
   enabled: true
   className: traefik
   host: nginx.demo.local
+
+# Names of the ConfigMap / Secret created by environments/<env>/configmap.yaml
+# and environments/<env>/secret.yaml
+configMap:
+  name: nginx-config-dev
+
+secret:
+  name: nginx-secret-dev