Check for predict-edits feature flag, remove is_staff check (#23165)

Release Notes:

- N/A

---------

Co-authored-by: Thorsten Ball <mrnugget@gmail.com>

crates/collab/src/llm.rs

@@ -440,8 +440,11 @@ async fn predict_edits(
     _country_code_header: Option<TypedHeader<CloudflareIpCountryHeader>>,
     Json(params): Json<PredictEditsParams>,
 ) -> Result<impl IntoResponse> {
-    if !claims.is_staff {
-        return Err(anyhow!("not found"))?;
+    if !claims.is_staff && !claims.has_predict_edits_feature_flag {
+        return Err(Error::http(
+            StatusCode::FORBIDDEN,
+            "no access to Zed's edit prediction feature".to_string(),
+        ));
     }
 
     let api_url = state