fix(ai-proxy): user cannot select their own model if one is defined

kong/plugins/ai-proxy/handler.lua

@@ -343,6 +343,13 @@ function _M:access(conf)
     return bad_request(err)
   end
 
+  -- check that the user isn't trying to override the plugin conf model in the request body
+  if request_table and request_table.model and type(request_table.model) == "string" then
+    if request_table.model ~= conf_m.model.name then
+      return bad_request("cannot use own model - must be: " .. conf_m.model.name)
+    end
+  end
+
   -- copy from the user request if present
   if (not multipart) and (not conf_m.model.name) and (request_table.model) then
     conf_m.model.name = request_table.model