Enable element call by default on sample config

Following the same logic from https://github.com/element-hq/element-web/pull/28314, this patch enables Element Call by default for other configs.

Downstream distributions that use the sample config should start using Element Call also!

Example: https://discourse.nixos.org/t/element-call-not-enabled-in-element-desktop/56077/3?u=yajo

config.sample.json

@@ -42,10 +42,13 @@
     "jitsi": {
         "preferred_domain": "meet.element.io"
     },
+    "features": {
+        "feature_video_rooms": true,
+        "feature_group_calls": true,
+        "feature_element_call_video_rooms": true
+    },
     "element_call": {
         "url": "https://call.element.io",
-        "participant_limit": 8,
-        "brand": "Element Call"
     },
     "map_style_url": "https://api.maptiler.com/maps/streets/style.json?key=fU3vlMsMn4Jb6dnEIFsx"
 }