Add configuration per administrative unit

[lagartoverde]

Overview

Add a way of adding configuration per administrative unit, in the future this will be replaced by user preferences and a call to the backend.
Also added the config needed to test lblod/ember-rdfa-editor-lblod-plugins#515

connected issues and PRs:

GN-5235
lblod/ember-rdfa-editor-lblod-plugins#515

Setup

None

How to test/reproduce

Login as Gemeente Gent, notice the style of the article titles is the old one. Then login as any other admin unit and notice we have the new article titles in there

Challenges/uncertainties

None

Checks PR readiness

• UI: works on smaller screen sizes
• UI: feedback for any loading/error states
• Check cancel/go-back flows
• Check database state correct when deleting/updating (especially regarding relationships)
• changelog
• npm lint
• no new deprecations

[elpoelma]

Looks good overall!

• There's a high chance OCMW Gent want this change as well, so we probably also want to add a config for them
• I know we do it in quite a few places, but I'm more of a fan to use URI's to identify resources instead of their IDs. URIs should be the same on every environment, but IDs could (technically) differ
• In the future we will probably want to move these configuration settings to a seperate ember-service (as more options will come and users will be able to edit them). Not needed now though.