🔥(backend) remove api managing templates

A complete API was able to manage templates lifecycle, from the creation
to the deletion and managing accesses on them. This API is not used by
the frontend application, is not finished. A connected user can interact
with this API and lead to unwanted behavior in the interface. Refering
ot issue #1222 templates can maybe totaly remove in the future. While
it's here and used, we only keep list and retrive endpoints. The
template management can still be done in the admin interface.

CHANGELOG.md

@@ -31,6 +31,10 @@ and this project adheres to
 
 - mitigate role escalation in the ask_for_access viewset #1580
 
+### Removed
+
+- 🔥(backend) remove api managing templates
+
 ## [3.9.0] - 2025-11-10
 
 ### Added