assistant: Add a Configuration page (#15490)

- [x] bug: setting a key doesn't update anything
- [x] show high-level text on configuration page to explain what it is
- [x] show "everything okay!" status when credentials are set
- [x] maybe: add "verify" button to check credentials
- [x] open configuration page when opening panel for first time and
nothing is configured
- [x] BUG: need to fix empty assistant panel if provider is `zed.dev`
but not logged in


Co-Authored-By: Thorsten <thorsten@zed.dev>

Release Notes:

- N/A

---------

Co-authored-by: Thorsten <thorsten@zed.dev>
Co-authored-by: Nate Butler <iamnbutler@gmail.com>
Co-authored-by: Thorsten Ball <mrnugget@gmail.com>

crates/language_model/src/language_model.rs

@@ -9,7 +9,7 @@ pub mod settings;
 use anyhow::Result;
 use client::Client;
 use futures::{future::BoxFuture, stream::BoxStream};
-use gpui::{AnyView, AppContext, AsyncAppContext, SharedString, Task, WindowContext};
+use gpui::{AnyView, AppContext, AsyncAppContext, FocusHandle, SharedString, Task, WindowContext};
 pub use model::*;
 use project::Fs;
 pub(crate) use rate_limiter::*;
@@ -84,7 +84,7 @@ pub trait LanguageModelProvider: 'static {
     fn load_model(&self, _model: Arc<dyn LanguageModel>, _cx: &AppContext) {}
     fn is_authenticated(&self, cx: &AppContext) -> bool;
     fn authenticate(&self, cx: &mut AppContext) -> Task<Result<()>>;
-    fn authentication_prompt(&self, cx: &mut WindowContext) -> AnyView;
+    fn configuration_view(&self, cx: &mut WindowContext) -> (AnyView, Option<FocusHandle>);
     fn reset_credentials(&self, cx: &mut AppContext) -> Task<Result<()>>;
 }