Callbacks created by application use http instead of https

In some cases this causes issues with security mechanisms like CSRF-tokens or URL validation of callback URLS.

We should consider setting the overwriteprotocol option to https.

https://docs.nextcloud.com/server/16/admin_manual/configuration_server/config_sample_php_parameters.html#proxy-configurations

Maybe we should also review the other proxy configuration values. like cli URL or overwritehost