Introduce slots or extension points to be able to edit custom user data

[netaddicts]

Looks we already have a table to store custom user data, but we don't yet have any option of editing the data from within the user workspace. It would be great to either have a slot where we can add extra web components or extension points so we could potentially have the user data being edited from the user workspace.
I'm sure we could introduce a new workspace, but if this is about editing a single property, makes sense to keep all (custom) user data editing experience in the same view
As a use case, we want to link a user to a specific translation user (external app)