Extract auto_update_ui crate (#21008)

This PR extracts an `auto_update_ui` crate out of the `auto_update`
crate.

This allows `auto_update` to not depend on heavier crates like `editor`,
which in turn allows other downstream crates to start building sooner.

Release Notes:

- N/A

crates/zed/Cargo.toml

@@ -23,6 +23,7 @@ assistant.workspace = true
 async-watch.workspace = true
 audio.workspace = true
 auto_update.workspace = true
+auto_update_ui.workspace = true
 backtrace = "0.3"
 breadcrumbs.workspace = true
 call.workspace = true