Display extension download counts (#7864)

This PR adds the download count for extensions to the extensions view.

Release Notes:

- Added download counts for extensions to the extensions view.

crates/extension/src/extension_store.rs

@@ -42,6 +42,7 @@ pub struct Extension {
     pub description: Option<String>,
     pub authors: Vec<String>,
     pub repository: String,
+    pub download_count: usize,
 }
 
 #[derive(Clone)]