Merge pull request #27416 from element-hq/rav/rust_migration_rollout_phase2b

Roll out Rust crypto to 30% of existing users on `app.element.io`

element.io/app/config.json

@@ -45,6 +45,6 @@
     "privacy_policy_url": "https://element.io/cookie-policy",
     "map_style_url": "https://api.maptiler.com/maps/streets/style.json?key=fU3vlMsMn4Jb6dnEIFsx",
     "setting_defaults": {
-        "RustCrypto.staged_rollout_percent": 10
+        "RustCrypto.staged_rollout_percent": 30
     }
 }