nightly url setting (#7037)

Release Notes:

- Added the ability to set settings per-release stage
- Added a `"server_url"` setting

crates/channel/src/channel_store_tests.rs

@@ -329,6 +329,7 @@ async fn test_channel_messages(cx: &mut TestAppContext) {
 fn init_test(cx: &mut AppContext) -> Model<ChannelStore> {
     let settings_store = SettingsStore::test(cx);
     cx.set_global(settings_store);
+    client::init_settings(cx);
 
     let http = FakeHttpClient::with_404_response();
     let client = Client::new(http.clone(), cx);