joyboy : feat: backend (#201)

* Init backend

* Init express

* http util

* Backend deposit claim endpoint

* Update contract address & Use env file

* Error Codes

* port env variable

* Move the backend to nextjs website

* Remove backend package

* fix lint

* Fix build errors

* Use ts paths

* ErrorCode type

* Remove env file and add to gitignore

https://github.com/keep-starknet-strange/joyboy/commit/e50ee4b1238470449ed7a903fba9896281b6289f