[AssetMapper] Re-configure "missing_import_mode" in prod/non-prod envs

Author: Kocal

symfony/asset-mapper/6.4/config/packages/asset_mapper.yaml

@@ -3,3 +3,9 @@ framework:
         # The paths to make available to the asset mapper.
         paths:
             - assets/
+        missing_import_mode: strict
+
+when@prod:
+    framework:
+        asset_mapper:
+            missing_import_mode: warn