feat: support showing image for chat message in NextJS (#368)

helpers/index.ts

.../types/streaming/nextjs/app/api/chat/llamaindex-stream.ts

templates/types/streaming/nextjs/app/api/chat/route.ts

...es/types/streaming/nextjs/app/components/chat-section.tsx

templates/types/streaming/nextjs/app/components/transform.ts

.../streaming/nextjs/app/components/ui/chat/chat-message.tsx

...streaming/nextjs/app/components/ui/chat/chat.interface.ts

...es/types/streaming/nextjs/app/components/ui/chat/index.ts