⚡ Introduce a new high-performing standalone chat API (#1200)

Closes #1154

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
	- Added authentication functionality for user sessions in chat API.
- Introduced chat-related API endpoints for starting, previewing, and
continuing chat sessions, and streaming messages.
- Implemented WhatsApp API webhook handling for receiving and processing
messages.
- Added environment variable `NEXT_PUBLIC_CHAT_API_URL` for chat API URL
configuration.

- **Bug Fixes**
	- Adjusted file upload logic to correctly determine the API host.
	- Fixed message streaming URL in chat integration with OpenAI.

- **Documentation**
- Updated guides for creating blocks, local installation, self-hosting,
and deployment to use `bun` instead of `pnpm`.

- **Refactor**
	- Refactored chat API functionalities to use modular architecture.
- Simplified client log saving and session update functionalities by
using external functions.
	- Transitioned package management and workflow commands to use `bun`.

- **Chores**
- Switched to `bun` for package management in Dockerfiles and GitHub
workflows.
	- Added new Dockerfile for chat API service setup with Bun framework.
	- Updated `.prettierignore` and documentation with new commands.

- **Style**
	- No visible changes to end-users.

- **Tests**
	- No visible changes to end-users.

- **Revert**
	- No reverts in this release.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

apps/viewer/src/app/api/v1/sessions/[sessionId]/streamMessage/route.ts

@@ -0,0 +1,45 @@
+import { getMessageStream } from '@typebot.io/bot-engine/apiHandlers/getMessageStream'
+import { StreamingTextResponse } from 'ai'
+import { NextResponse } from 'next/server'
+
+export const dynamic = 'force-dynamic'
+
+const responseHeaders = {
+  'Access-Control-Allow-Origin': '*',
+  'Access-Control-Allow-Methods': 'POST, OPTIONS',
+  'Access-Control-Expose-Headers': 'Content-Length, X-JSON',
+  'Access-Control-Allow-Headers': '*',
+}
+
+export async function OPTIONS() {
+  return new Response('ok', {
+    headers: {
+      'Access-Control-Allow-Origin': '*',
+      'Access-Control-Allow-Methods': 'POST',
+      'Access-Control-Expose-Headers': 'Content-Length, X-JSON',
+      'Access-Control-Allow-Headers': '*',
+    },
+  })
+}
+
+export async function POST(
+  req: Request,
+  { params }: { params: { sessionId: string } }
+) {
+  if (process.env.VERCEL_ENV)
+    return NextResponse.json(
+      { message: "Can't get streaming if hosted on Vercel" },
+      { status: 400, headers: responseHeaders }
+    )
+  const messages =
+    typeof req.body === 'string' ? JSON.parse(req.body) : req.body
+  const { stream, status, message } = await getMessageStream({
+    sessionId: params.sessionId,
+    messages,
+  })
+  if (!stream)
+    return NextResponse.json({ message }, { status, headers: responseHeaders })
+  return new StreamingTextResponse(stream, {
+    headers: responseHeaders,
+  })
+}