Fix EZP-23552: Symfony cache won't be cleaned if Legacy ViewCaching is disabled

> https://jira.ez.no/browse/EZP-23552

This enforces `ViewCaching` to be enabled when going through Symfony.
This is mandatory for persistence/HTTP cache to be correctly cleared.

To avoid pitfalls with having ViewCaching always enabled (e.g. having to clear cache on each change in a legacy template), one might just enable `site.ini/TemplateSettings/DevelopmentMode`:

```ini
[TemplateSettings]
DevelopmentMode=enabled
```
Nitpick mode engage: "...in order for..."
+1