Move moderator role to Keycloak

[hangy]

Who for

As an administrator,

What

I want to be able to mark users as moderators in Keycloak,

Why

so that this permission is saved globally and available to all clients.

How (rough idea)

• Read https://www.keycloak.org/docs/25.0.2/server_admin/#assigning-permissions-using-roles-and-groups
• Create new realm roles for moderators and for "producer platform moderators" in Keycloak
• Create new groups for moderators and for "producer platform moderators" in Keycloak
• Update Product Opener to use the new OIDC scope (from the roles) when checking the current user's permissions
• Write a script like https://github.com/openfoodfacts/openfoodfacts-server/blob/b0d675c79eb6b81bc77e30489dca25742dd5e490/scripts/migrate_users_to_keycloak.pl to migrate existing moderator permissions to Keycloak using the Keycloak Admin REST API