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/app_menus.rs

@@ -21,6 +21,7 @@ pub fn app_menus() -> Vec<Menu<'static>> {
                         MenuItem::action("Select Theme", theme_selector::Toggle),
                     ],
                 }),
+                MenuItem::action("Extensions", extensions_ui::Extensions),
                 MenuItem::action("Install CLI", install_cli::Install),
                 MenuItem::separator(),
                 MenuItem::action("Hide Zed", super::Hide),