Keycloak database entries on first load (OIDC_RESOLVE_USER_FUNCTION)

[reinoudbaker]

This bug appears on the initial load of a user (i.e. when the models.KeyCloak is not yet persisted to db) . When firing two simulatious request on function backend.get_user_by_id can raise an IntegrityError exception (duplicate key in models.KeyCloak) on line 157 of bossoidc.backend

suggested fix:
change
kc_user = KeycloakModel.objects.create(user = user, UID = uid)
to:
kc_user, created = KeycloakModel.objects.get_or_create(user = user, UID = uid)