feat(template): Write operator file logs to an emptyDir under /var/log

This makes it possible for us to switch to a read-only root filesystem.
And it causes the logs to survive a container restart.

Author: lfrancke

template/deploy/helm/[[operator]]/templates/_telemetry.tpl.j2

@@ -1,3 +1,10 @@
+{{/*
+Shared by FILE_LOG_DIRECTORY and the log volume mount in deployment.yaml, which have to agree.
+*/}}
+{{- define "{[ operator.name }].telemetry.fileLogDirectory" -}}
+/var/log/{{ include "{[ operator.name }].appname" . }}
+{{- end }}
+
 {{/*
 Create a list of telemetry related env vars.
 */}}
@@ -17,7 +24,7 @@ Create a list of telemetry related env vars.
 {{ end }}
 {{- if .fileLog.enabled }}
 - name: FILE_LOG_DIRECTORY
-  value: /stackable/logs/{{ include "{[ operator.name }].appname" $ }}
+  value: {{ include "{[ operator.name }].telemetry.fileLogDirectory" $ }}
 {{- end }}
 {{- if and .fileLog.enabled .fileLog.level }}
 - name: FILE_LOG_LEVEL

template/deploy/helm/[[operator]]/templates/deployment.yaml.j2

@@ -103,6 +103,11 @@ spec:
             periodSeconds: 3
             failureThreshold: 30
             timeoutSeconds: 3
+          {{- if .Values.telemetry.fileLog.enabled }}
+          volumeMounts:
+            - name: log
+              mountPath: {{ include "{[ operator.name }].telemetry.fileLogDirectory" . }}
+          {{- end }}
       {{- with .Values.nodeSelector }}
       nodeSelector:
         {{- toYaml . | nindent 8 }}
@@ -118,6 +123,11 @@ spec:
       {{- with .Values.priorityClassName }}
       priorityClassName: {{ . }}
       {{- end }}
+      {{- if .Values.telemetry.fileLog.enabled }}
+      volumes:
+        - name: log
+          emptyDir: {}
+      {{- end }}
 {[% else %}]
 # Templated Deployment disabled for this operator
 {[% endif %}]