Add initial user API

[darshanasbg]

Purpose

This pull request introduces a new user management feature to the backend system. It includes database schema updates for both PostgreSQL and SQLite, a new UserService with REST API endpoints, and supporting models, handlers, and data storage logic. Below are the most important changes grouped by theme:

Database Schema Updates

• Added a new USER table to both PostgreSQL (postgress.sql) and SQLite (sqlite.sql) schemas to store user details such as USER_ID, ORG_ID, TYPE, and ATTRIBUTES. The table includes timestamps for CREATED_AT and UPDATED_AT. [1] [2]
• Inserted a sample user record into the USER table in both PostgreSQL and SQLite scripts. [1] [2]

Service Layer Implementation

• Introduced a new UserService in userservice.go to handle user-related operations, including creating, retrieving, updating, and deleting users. The service is registered in the ServiceManager. [1] [2]

REST API for User Management

• Added a UserHandler in userhandler.go to define REST API endpoints (POST, GET, PUT, DELETE) for user management. Each endpoint is mapped to a corresponding service method.

Supporting Models and Providers

• Created a User model in user.go to represent user data, including Id, OrgId, Type, and Attributes.
• Added a UserProvider in userprovider.go to abstract the creation and retrieval of the UserService instance.

Data Storage Layer

• Defined SQL queries for user operations (create, retrieve, update, delete) in constants.go under the store package. These queries are used by the UserService to interact with the database.