✨(backend) add user abilities for front

This allows, on a per user basis, the display of
features.

The main goal here is to allow Team admin or owner
to see the management views.
We also added the same for the two other features
(mailboxes and contacts)

This will be improved later if needed :)

src/backend/core/models.py

@@ -440,6 +440,63 @@ class User(AbstractBaseUser, BaseModel, auth_models.PermissionsMixin):
             raise ValueError("You must first set an email for the user.")
         mail.send_mail(subject, message, from_email, [self.email], **kwargs)
 
+    def get_abilities(self):
+        """
+        Return the user permissions at the application level (ie feature availability).
+
+        Note: this is for display purposes only for now.
+
+        - Contacts view and creation is globally available (or not) for now.
+        - Teams view is available if the user is owner or admin of at least
+        one Team for now. It allows to restrict users knowing the existence of
+        this feature.
+        - Teams creation is globally available (or not) for now.
+        - Mailboxes view is available if the user has access to at least one
+        MailDomain for now. It allows to restrict users knowing the existence of
+        this feature.
+        - Mailboxes creation is globally available (or not) for now.
+        """
+        user_info = (
+            self._meta.model.objects.filter(pk=self.pk)
+            .annotate(
+                teams_can_view=models.Exists(
+                    self.accesses.model.objects.filter(  # pylint: disable=no-member
+                        user=models.OuterRef("pk"),
+                        role__in=[RoleChoices.OWNER, RoleChoices.ADMIN],
+                    )
+                ),
+                mailboxes_can_view=models.Exists(
+                    self.mail_domain_accesses.model.objects.filter(  # pylint: disable=no-member
+                        user=models.OuterRef("pk")
+                    )
+                ),
+            )
+            .only("id")
+            .get()
+        )
+
+        teams_can_view = user_info.teams_can_view
+        mailboxes_can_view = user_info.mailboxes_can_view
+
+        return {
+            "contacts": {
+                "can_view": settings.FEATURES["CONTACTS_DISPLAY"],
+                "can_create": (
+                    settings.FEATURES["CONTACTS_DISPLAY"]
+                    and settings.FEATURES["CONTACTS_CREATE"]
+                ),
+            },
+            "teams": {
+                "can_view": teams_can_view and settings.FEATURES["TEAMS"],
+                "can_create": teams_can_view and settings.FEATURES["TEAMS_CREATE"],
+            },
+            "mailboxes": {
+                "can_view": mailboxes_can_view,
+                "can_create": mailboxes_can_view
+                and settings.FEATURES["MAILBOXES_CREATE"],
+            },
+        }
+
 
 class OrganizationAccess(BaseModel):
     """