Add backend model endpoints for UI interaction

[nerdalert]

todo:

• [x] update ui/.env.example
• [x] resolve lint checks
• [x] fix the copy button in chat output
• [x] add a dev playground
• [x] consolidate chats and swap models with a dropdown
• [x] enable custom openai api endpoints with local storage (ex. local or remote ilab instance)
• [ ] add a couple of other languages to show code

[vishnoianil]

Minor comments, otherwise LGTM

[nerdalert]

• Adds a dev playground for building custom queries and export them as code.
• Adds the ability to add a custom IL (or any openai api) endpoint.
• Added model switching drop-down.

https://github.com/instructlab/instructlab-bot/assets/1711674/c2db3427-f8f7-4ec8-b2d0-06e0aae2d21e