Support zscaler

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### Feature description
Right now Nextcloud Desktop is not able to work on a client using zscaler as company-proxy. There are probably two reasons for that:
1. You use another certificate store other then Windows - see https://help.zscaler.com/zia/adding-custom-certificate-application-specific-trust-store
2. If zscaler does not categorize your server/instance, you could still go on (like in my case), but you can't click "Continue" using Nextcloud Desktop