onboarding: Create basic onboarding page (#34723)

Release Notes:

- N/A

---------

Co-authored-by: Ben Kunkle <ben@zed.dev>

crates/zed/src/zed.rs

@@ -3957,6 +3957,7 @@ mod tests {
             language::init(cx);
             workspace::init(app_state.clone(), cx);
             welcome::init(cx);
+            onboarding::init(cx);
             Project::init_settings(cx);
             app_state
         })