etcd chart: additional env vars for etcd pods

Allows extra environment variables to be applied to the etcd pods. Can
be used to apply tuning parameters, enable experimental flags, etc.

Change-Id: I9d82514b6e3a292edc472d885c0a61d5c81199f5

charts/etcd/templates/etc/_kubernetes-etcd.yaml.tpl

@@ -123,6 +123,7 @@ spec:
           value: https://$(POD_IP):{{ .Values.network.service_peer.target_port }}
         - name: MANIFEST_PATH
           value: /manifests/{{ .Values.service.name }}.yaml
+{{ include "helm-toolkit.utils.to_k8s_env_vars" .Values.pod.env.etcd | indent 8 }}
 {{ dict "envAll" $envAll "component" "etcd" "container" "etcd" "type" "readiness" "probeTemplate" (include "etcdreadinessProbeTemplate" $envAll | fromYaml) | include "helm-toolkit.snippets.kubernetes_probe" | indent 6 }}
 {{ dict "envAll" $envAll "component" "etcd" "container" "etcd" "type" "liveness" "probeTemplate" (include "etcdlivenessProbeTemplate" $envAll | fromYaml) | include "helm-toolkit.snippets.kubernetes_probe" | indent 6 }}
       volumeMounts:

charts/etcd/values.yaml

@@ -188,6 +188,13 @@ pod:
     # requires override for a specific use case e.g. calico-etcd or kubernetes-etcd
     example-etcd:
       etcd: localhost/docker-default
+  env:
+    etcd:
+      # can be used for tuning, e.g. https://etcd.io/docs/v3.4.0/tuning/
+      # or other flags, e.g. https://etcd.io/docs/v3.4.0/op-guide/configuration/
+      # ETCD_HEARTBEAT_INTERVAL: 100
+      # ETCD_ELECTION_TIMEOUT: 1000
+      # ETCD_SNAPSHOT_COUNT: 10000
 
 jobs:
   etcd_backup: