Add chat tab

[csaroff]

I've been wanting to see a chat interface in nat.dev for a while and decided to try to push this over the line. Big thanks to @max for the excellent scaffolding.

This adds a chat tab to open-playground integrated with AI completions. It also integrates with the history sidebar so that you can refer back to old conversations.

I'm not a frontend expert so the css might be a bit rough around the edges. I also didn't fully flush out the typescript typings that max had started. I figured a minimally working chat tab was better than none, but let me know if there's anything you'd like to see added/changed as a part of this PR.

In the future it might be cool to add:

1. A "new chat" button in the history sidebar(for now, just refresh the page).
2. A button to show/hide the chat history.
3. The ability to edit a previous message and rerun the completion on an old prompt.
4. Logos/Avatars for the AI models and the user.
5. Syntax Highlighting for markdown rendered code.
6. Threads to allow multiple models to answer the same question.
7. Some type of recursive summarization in case the conversation goes on past the context window.

[csaroff]

@max would love your feedback and blessing if you get a chance to take a look

[AlexanderLourenco]

@csaroff Would you mind coming on Discord?