Show current plan in user menu (#15513)

This PR updates the user menu to show the user's current plan.

Also adds a new RPC message to send this information down to the client
when Zed starts.

This is behind a feature flag.

Release Notes:

- N/A

---------

Co-authored-by: Max <max@zed.dev>

crates/zed_actions/src/lib.rs

@@ -26,6 +26,7 @@ actions!(
     zed,
     [
         OpenSettings,
+        OpenAccountSettings,
         Quit,
         OpenKeymap,
         About,