feat: Allow customizing the responses, flows in Captain (#11385)

- Ability to provide custom instructions to captain

<img width="1107" alt="Screenshot 2025-04-28 at 6 11 43 PM"
src="https://github.com/user-attachments/assets/f94cbccc-b4d8-48fd-b6b9-55524129bc50"
/>

config/routes.rb

@@ -53,6 +53,9 @@ Rails.application.routes.draw do
           end
           namespace :captain do
             resources :assistants do
+              member do
+                post :playground
+              end
               resources :inboxes, only: [:index, :create, :destroy], param: :inbox_id
             end
             resources :documents, only: [:index, :show, :create, :destroy]