[FIX] point_of_sale: make background loading silent

Loading in background is supposed be background and not block UI after 3 sec of
loading.

STEPS:
* In `pos.config` set `[x] Limited Products Loading`, and `[x] ​Load all
remaining products in the background`
* add enough products to POS, e.g. 40 000
* Open pos

BEFORE: background loading triggers UI Blocking if it takes more than 3 seconds
AFTER:  products/partners are loaded in background without interrupting UI

---

opw-2817770

closes odoo/odoo#88330

X-original-commit: 64232893886c6613212885a382b6f0732c091ef2
Signed-off-by: Masereel Pierre <pim@odoo.com>

addons/point_of_sale/static/src/js/models.js

@@ -437,7 +437,7 @@ class PosGlobalState extends PosModel {
                     offset: page * this.config.limited_products_amount,
                     limit: this.config.limited_products_amount,
                 }],
-            });
+            }, { shadow: true });
             this._loadProductProduct(products);
             page += 1;
         } while(products.length == this.config.limited_products_amount);
@@ -459,7 +459,7 @@ class PosGlobalState extends PosModel {
                     },
                 ],
                 context: this.env.session.user_context,
-            });
+            }, { shadow: true });
             this.db.add_partners(partners);
             i += 1;
         } while(partners.length);