Comp 282 add observer role

This MR adds the observer role. The main difference is that observers cannot be assigned to an NREN (the assignment is ignored) - and observers have read-only access to all surveys.

The landing page for observers has a table which lists links to the latest survey to each NREN, instead of directly navigating to a specific survey.

compendium_v2/db/auth_model.py

@@ -23,6 +23,7 @@ logger = logging.getLogger(__name__)
 class ROLES(Enum):
     admin = "admin"
     user = "user"
+    observer = "observer"
 
 
 uuid_pk = Annotated[UUID, mapped_column(primary_key=True, default=lambda _: uuid4())]
@@ -74,6 +75,10 @@ class User(UserMixin, db.Model):
     def is_admin(self):
         return self.roles == ROLES.admin
 
+    @property
+    def is_observer(self):
+        return self.roles == ROLES.observer
+
     @property
     def nren(self):
         if len(self.nrens) == 0: