PaaS Document shopware configuration changes

[TrayserCassa]

Document the configuration of shopware specific configuration as file in the repository itself.

As described in https://docs.shopware.com/de/shopware-6-de/tutorials-und-faq/html-sanitizer at the end, we would like to deactivate the "html_sanitizer".
For "self-hosted", the addition in z-shopware.yaml is suggested

shopware:
 html_sanitizer:
 enabled: false