Keycloak theme

[lmarini]

Create a Keycloak them for the authetication pages and figure out a way to load it into the keycloak docker container.

https://www.keycloak.org/docs/latest/server_development/#_themes

This helps create themes in React https://github.com/InseeFrLab/keycloakify. If I understand it correctly it just makes it possible to use the same components as your app. It might be extra work and since our app uses the default MUI material ui for now it might overkill.