Add Element Call `brand` (#23443)

config.sample.json

@@ -45,7 +45,8 @@
         "preferred_domain": "meet.element.io"
     },
     "element_call": {
-        "url": "https://call.element.io"
+        "url": "https://call.element.io",
+        "brand": "Element Call"
     },
     "map_style_url": "https://api.maptiler.com/maps/streets/style.json?key=fU3vlMsMn4Jb6dnEIFsx"
 }

docs/config.md

@@ -323,6 +323,8 @@ The VoIP and Jitsi options are:
       and may be removed at any time without notice. Defaults to `https://call.element.io`.
    - `use_exclusively`: A boolean specifying whether Element Call should be used exclusively as the only VoIP stack in
       the app, removing the ability to start legacy 1:1 calls or Jitsi calls. Defaults to `false`.
+   - `brand`: Optional name for the app. Defaults to `Element Call`. This is
+     used throughout the application in various strings/locations.
 
 ## Bug reporting