Add an extensions installation view (#7689)

This PR adds a view for installing extensions within Zed.

My subtasks:

- [X] Page Extensions and assign in App Menu
- [X] List extensions 
- [X] Button to Install/Uninstall
- [x] Search Input to search in extensions registry API
- [x] Get Extensions from API
- [x] Action install to download extension and copy in /extensions
folder
- [x] Action uninstall to remove from /extensions folder
- [x] Filtering
- [x] Better UI Design

Open to collab!

Release Notes:

- Added an extension installation view. Open it using the `zed:
extensions` action in the command palette
([#7096](https://github.com/zed-industries/zed/issues/7096)).

---------

Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>
Co-authored-by: Marshall <marshall@zed.dev>
Co-authored-by: Carlos <foxkdev@gmail.com>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>
Co-authored-by: Max <max@zed.dev>

crates/zed/src/zed.rs

@@ -2396,6 +2396,7 @@ mod tests {
                 .unwrap()
         }
     }
+
     fn init_keymap_test(cx: &mut TestAppContext) -> Arc<AppState> {
         cx.update(|cx| {
             let app_state = AppState::test(cx);
@@ -2409,6 +2410,7 @@ mod tests {
             app_state
         })
     }
+
     #[gpui::test]
     async fn test_base_keymap(cx: &mut gpui::TestAppContext) {
         let executor = cx.executor();