fix(accounts): knox creates no table of its own

knox's first migration creates its AuthToken table even when
KNOX_TOKEN_MODEL replaces it with accounts.ApiToken. The unused
knox_authtoken table references auth_user, and Django, which does not see
it, does not empty it with the others: on PostgreSQL every test that
empties the database failed ("cannot truncate a table referenced in a
foreign key constraint"). SQLite does not check this, so only CI's
PostgreSQL leg showed it. knox stays installed for its token code, with
its migrations turned off (MIGRATION_MODULES).

webvirtcloud/settings.py.template

@@ -381,6 +381,9 @@ REST_FRAMEWORK = {
 # "Authorization: Token wvc_..."; made and deleted on the profile page
 KNOX_TOKEN_MODEL = "accounts.ApiToken"
 REST_KNOX = {"TOKEN_PREFIX": "wvc_"}
+# knox stays installed for its token code, but its migrations would create a
+# knox_authtoken table that accounts.ApiToken replaces
+MIGRATION_MODULES = {"knox": None}
 
 SPECTACULAR_SETTINGS = {
     "TITLE": "Webvirtcloud REST-API",