Monorepo setup with shared types

[donljh]

• Moving from npm and using pnpm as our package manager instead since they offering much better experience with workspaces. Some QOL changes, (1) pnpm i at the root to install all dependencies -- pnpm lifts up common dependencies to the root level, so no need to deal with package-lock.json at the individual subfolder level, only 1 pnpm-lock.yaml at the root level (2) pnpm dev at the root level now runs the dev script for frontend and question service

• Created a common types package under common/shared-types, we can put our Request / Response types here and share them between front and backend

• Standardise the location of the firebase json file and name under .firebase, which is git-ignored

[Cloud7050]

Will take a closer look while merging into qcon branch, and update pending changes there accordingly.