Make preferences visible for non-admins via admin privileges

[bentuna]

Feature request

Which Nextcloud Version are you currently using: 32.0.3

Is your feature request related to a problem? Please describe.
The welcome message is more of a marketing or customer service people task, so it is unfortunate that it can be edited by admins only for now.

Describe the solution you'd like
When you give a group of users admin privileges via /settings/admin/admindelegation, they should see the preferences for the welcome widget under /settings/admin/theming as well as being able to edit them.

[janepie]

Sounds like a good idea! We'd be happy to receive a PR for that, the needed changes are described in https://docs.nextcloud.com/server/25/developer_manual/basics/setting.html