Implement secure cloud sandboxes with E2B (#35)

* chore: rename utils.ts to fileoperations.ts

* feat: replace node-pty with E2B sandboxes

* added debounced function in the editor

* fix: move socket connection to useRef

* fix: wait until terminals are killed to close the container

* fix: ensure container remains open until all owner connections are closed

* fix: sync files to container instead of local file system

* fix: set project file permissions so that they belong to the terminal user

* fix: use the container URL for the preview panel

* fix: count only the current user's sandboxes towards the limit

* fix: remove hardcoded reference to localhost

* fix: add error handling to the backend

* docs: add information about E2B

---------

Co-authored-by: Akhilesh Rangani <akhileshrangani4@gmail.com>

backend/server/.env.example

@@ -5,3 +5,4 @@ PORT=4000
 WORKERS_KEY=
 DATABASE_WORKER_URL=
 STORAGE_WORKER_URL=
+E2B_API_KEY=