[ANT-964] Add user preference pages

[pl-buiquang]

In the configuration section add a new subsection for user preferences (which should be the first tab). The title of this page is "Preferences" It should display (for now):

• the user name
• the language preference (en or fr)

In the backend, user preferences will be stored in the ConfigData table, so a new endpoint to put and retrieve values in this user's key-value store must be added.

[create-issue-branch[bot]]

Branch feature/pl-buiquang/issue-960-Add_user_preference_pages created!

[laurent-laporte-pro]

The preferences could also store the last used study, but the user interface must also be able to automatically display the edit page for that study.