Update alpine Docker tag to v3.15.0

Author: renovate-bot

charts/envoy/values.yaml

@@ -3,7 +3,7 @@ initContainer:
     # initContainer.image.repository -- initContainer image repository
     repository: alpine
     # initContainer.image.tag -- initContainer image tag
-    tag: 3.12.4
+    tag: 3.15.0
     # initContainer.image.pullPolicy -- initContainer image pull policy
     pullPolicy: IfNotPresent
   command: "apk add perl && cp /opt/envoy.yaml.tpl /config/envoy.yaml && perl -pi -e 's/ENV_([_A-Z0-9]+)_ENV/$ENV{$1}/g' /config/envoy.yaml"