Feature: add room threads list (#6575)

Add threads list screen for rooms:

- Add `ThreadsListService` to subscribe to thread changes in the room.
- Create `ThreadsListView` and its associated node a presenters (the UI may change).
- Add a menu icon in the room screen to open it.

This is still pending info about unread threads, so several UI components related to it will be hidden.

* Add feature flag and use it to hide the access to this new screen

---------

Co-authored-by: ElementBot <android@element.io>

libraries/featureflag/api/src/main/kotlin/io/element/android/libraries/featureflag/api/FeatureFlags.kt

@@ -155,4 +155,11 @@ enum class FeatureFlags(
         defaultValue = { false },
         isFinished = false,
     ),
+    RoomThreadList(
+        key = "feature.room_thread_list",
+        title = "Add a list of threads in a room",
+        description = "Add a new screen with a list of threads in a room.",
+        defaultValue = { false },
+        isFinished = false,
+    ),
 }