[BE Feat] Setup and create common shared data structures and objects

[SherRao]

Checklist

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Description

These are various constants, errors, helpers, responses, and requests that can be reused through the backend.

Requirements

Constants

• x

Errors

• x

Helpers

• x

Responses

• x

Requests

• x

[juancwu]

These are values in the server package. So we can just create empty files. For requests and responses, these are meant to be super generic structs that any route can just use.