Introduce monorepo to manage packages

[gwbaik9717]

What would you like to be added:

Introduce a monorepo structure to manage the frontend and backend packages efficiently.

Why is this needed:

Implementing a monorepo in Coedepair will simplify and streamline package management across the project. Given that both the frontend and backend are built using TypeScript, adopting a monorepo will allow us to maximize code sharing and consistency across the codebase.

Additional Information:
There are several options available for setting up a monorepo, including lerna, turborepo, and pnpm. Among these, pnpm might be great option due to several reasons:

1. Given that our sibling project, Yorkie-JS-SDK, is already using pnpm to manage its monorepo, it would be advantageous to align our approach for consistency.
2. "Turborepo is a good one but its key feature "task cache" requires Vercel or a self-hosted cache server. If we think the benefit of having a remote build cache is significant, then Turborepo would be good, if not, pnpm is good to go." by @blurfx

Related to: yorkie-team/yorkie-js-sdk#648

[devleejb]

Considering the consistency in the management area, pnpm seems like a good choice.