feat(types): adding modelSelection flag in ChatOptions for server to … (#566)

* feat(types): adding modelSelection flag in ChatOptions for server to tell clients if model selection is supported

* chore: add comment for modelSelextion

Author: XiaoxuanLu

types/chat.ts

@@ -244,6 +244,11 @@ export interface ChatOptions {
 
     mcpServers?: boolean
 
+    /**
+     * Server signals to Chat Client support of model selection.
+     */
+    modelSelection?: boolean
+
     /**
      * Server signals to Chat Client support of conversation history.
      */