Update docker env, fix config_cache. Fixes #5033

.env.docker

@@ -60,6 +60,15 @@ ADMIN_DOMAIN="${APP_DOMAIN}"
 # @dottie/validate required,boolean
 #APP_DEBUG="false"
 
+# Disable config cache
+#
+# If disabled, settings must be managed by .env variables.
+#
+# @default "false"
+# @see https://docs.pixelfed.org/technical-documentation/config/#config_cache
+# @dottie/validate required,boolean
+ENABLE_CONFIG_CACHE="false"
+
 # Enable/disable new local account registrations.
 #
 # @default "true"