Allow dark mode to be set on a user basis

[Alphayeeeet]

Describe the feature:
Currently a space admin can toggle dark mode per space. Default is to disable dark mode. However if the setting is changed, dark mode applies to all users of that space. Currently there are no possibilities to achieve customizing this per user. This should be changed, so that a user can define their own preference to either use dark mode or light mode.

Describe a specific use case for the feature:
It would be a UX benefit for the end user.

[ThomThomson]

This feature was added in 8.8.0 in #151507.

Closing this issue as completed. Thank you for your contribution!

[Alphayeeeet]

@ThomThomson Is there any privilege which restricts those settings. I couldn't find any doc for this topic.
Our superuser can see those settings however the personal users cannot.

[Alphayeeeet]

@ThomThomson I've done some testing and it might be due our automatic user creation using the Elasticsearch API. Users created via the Elasticsearch API cannot see those settings