Add secret support for filer environment variables. (#4538)

Instead of providing a literal value as a string, you can provide the contents of valueFrom as a map.

k8s/charts/seaweedfs/templates/filer-statefulset.yaml

@@ -88,7 +88,12 @@ spec:
             {{- if .Values.filer.extraEnvironmentVars }}
             {{- range $key, $value := .Values.filer.extraEnvironmentVars }}
             - name: {{ $key }}
+            {{- if kindIs "string" $value }}
               value: {{ $value | quote }}
+            {{- else }}
+              valueFrom:
+                {{ toYaml $value | nindent 16 | trim }}
+            {{- end -}}
             {{- end }}
             {{- end }}
             {{- if .Values.global.extraEnvironmentVars }}