assistant: Limit model access for Zed AI users to Claude-3.5-sonnet (#15904)

This prevents users from accessing other models, such as OpenAI's GPT-4
or Google's Gemini-Pro.
Staff members can still access all models.

Co-authored-by: Thorsten <thorsten@zed.dev>

Release Notes:

- N/A

---------

Co-authored-by: Thorsten <thorsten@zed.dev>

crates/collab/src/llm/token.rs

@@ -13,13 +13,19 @@ pub struct LlmTokenClaims {
     pub exp: u64,
     pub jti: String,
     pub user_id: u64,
+    pub is_staff: bool,
     pub plan: rpc::proto::Plan,
 }
 
 const LLM_TOKEN_LIFETIME: Duration = Duration::from_secs(60 * 60);
 
 impl LlmTokenClaims {
-    pub fn create(user_id: UserId, plan: rpc::proto::Plan, config: &Config) -> Result<String> {
+    pub fn create(
+        user_id: UserId,
+        is_staff: bool,
+        plan: rpc::proto::Plan,
+        config: &Config,
+    ) -> Result<String> {
         let secret = config
             .llm_api_secret
             .as_ref()
@@ -31,6 +37,7 @@ impl LlmTokenClaims {
             exp: (now + LLM_TOKEN_LIFETIME).timestamp() as u64,
             jti: uuid::Uuid::new_v4().to_string(),
             user_id: user_id.to_proto(),
+            is_staff,
             plan,
         };