[Enh]: Avoid Privacy-Leaks (multiple) by default

Description

I am trying to operate a private Nextcloud instance. I find that there are many features such as update notifications or the updating of contact avatars from social media that trade off privacy for convenience. I kindly ask you to adopt a development rule:

No server-side fetching of external resources/URL without explicit permission.

A few examples:

• default to not check automatically update channel and do not notify about availability of updates. default can be overridden by admin. offer instead a side-channel such as a mailing list to which admins can subscribe and that sends out very short, simple, plain text notifications. not the marketing-polished text i recently saw in my inbox and motivated me to unsubscribe.
• default to not allow update of contacts avatars from social media. default can be overridden by admin, and if admin overrides, each user can still turn on/off for themselves.
• default to not searching global and public address book
• default new installations of the Calendar server to not send invitations/notifications

defaults matter and should be chosen for privacy first, not for convenience. even when that privacy is less beneficial to the Nextcloud project (Usage survey). put your users' privacy first and you will be rewarded with more trust. there is nothing wrong with guiding the users to change the defaults, explaining the benefits/costs trade-off.

Steps to reproduce

1.Install a new Nextcloud instance with default settings
2.watch for the instance's fetching of external URLs

Expected behavior

no fetching of external URL that has not been previously consented to by the instance admin.

The issue names no files, tests, or entry points, so begin by inventorying the cited behaviors across the Nextcloud server and identifying their current defaults and consent paths. Done would require a maintainer-defined, scoped set of privacy-default changes with tests covering external URL fetching and administrator or user overrides.