Add auto-update system for extensions (#9890)

* [x] auto update extensions on startup
* [ ] add a manual way of updating all?
* [x] add a way to opt out of auto-updates for a particular extension

We don't believe that there should be any background polling for
extension auto-updates, because it could be disruptive to the user.

Release Notes:

- Added an auto-update system for extensions.

---------

Co-authored-by: Marshall <marshall@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>

crates/activity_indicator/src/activity_indicator.rs

@@ -1,5 +1,6 @@
 use auto_update::{AutoUpdateStatus, AutoUpdater, DismissErrorMessage};
 use editor::Editor;
+use extension::ExtensionStore;
 use futures::StreamExt;
 use gpui::{
     actions, svg, AppContext, CursorStyle, EventEmitter, InteractiveElement as _, Model,
@@ -288,6 +289,18 @@ impl ActivityIndicator {
             };
         }
 
+        if let Some(extension_store) =
+            ExtensionStore::try_global(cx).map(|extension_store| extension_store.read(cx))
+        {
+            if let Some(extension_id) = extension_store.outstanding_operations().keys().next() {
+                return Content {
+                    icon: Some(DOWNLOAD_ICON),
+                    message: format!("Updating {extension_id} extension…"),
+                    on_click: None,
+                };
+            }
+        }
+
         Default::default()
     }
 }