🧑‍💻(demo) improve distribution in number of identities per user

The current implementation of our product demo via the make command lacks
user identity for a significant portion of generated users, limiting the
realism of the showcased scenarios. As it stands, users created by the make
command lack complete information, such as full names and email addresses,
because they don't have any identity.

I tried to come up with the simplest solution:
We now generate a very small portion of our users with 0 identities. The
probability for users to have only 1 identity is the highest but they
can have up to 4 with decreasing probabilities. I removed the possibility
to set a maximum number of identities as it doesn't bring any value.

3% percent of the identities created will have no email and 3% no name.

Fixes https://github.com/numerique-gouv/people/issues/90

src/backend/demo/defaults.py

@@ -3,6 +3,5 @@
 NB_OBJECTS = {
     "users": 1000,
     "teams": 100,
-    "max_identities_per_user": 3,
     "max_users_per_team": 100,
 }

src/backend/demo/management/commands/create_demo.py

@@ -129,16 +129,19 @@ def create_demo(stdout):
         users_values = list(models.User.objects.values("id", "email"))
         for user_dict in users_values:
             for i in range(
-                random.randint(0, defaults.NB_OBJECTS["max_identities_per_user"])
+                random.choices(range(5), weights=[5, 50, 30, 10, 5], k=1)[0]
             ):
                 user_email = user_dict["email"]
                 queue.push(
                     models.Identity(
                         user_id=user_dict["id"],
                         sub=uuid4(),
-                        email=f"identity{i:d}{user_email:s}",
                         is_main=(i == 0),
-                        name=fake.name(),
+                        # Leave 3% of emails and names empty
+                        email=f"identity{i:d}{user_email:s}"
+                        if random.random() < 0.97
+                        else None,
+                        name=fake.name() if random.random() < 0.97 else None,
                     )
                 )
         queue.flush()