Establish the project structure and implements User context

[nyeong]

Context

refer: #1, #2.

Goal

• [x] establish the project structure.
  • unit tests and e2e tests for the user context.
• [x] implements user context.
  • authenticate users via JWT.
  • CRU- for users.

Detailed

• Separates the contexts by endpoints.
  • User context covers authentication, registration, getCurrentUser and updateUser.
• All tests are located in the /test directory.
  • E2E tests are located with the name like: user.e2e-spec.ts.
  • We can test e2e test cases with npm run test:e2e.
  • E2E tests use sqlite in-memory database for speed. The config is located in /config/typeorm.config.ts.
  • Unit tests are located in the directory named after the contexts. (ex: /test/user/user.controller.spec.ts)
  • We can test unit test cases with npm run test.
• Authenticates the user via JWT using @nestjs/jwt.
  • The config is located in /config/jwt.config.ts.
  • You can verify the token using AuthMiddleware andAuthGuard. Check user.module.ts.
  • You can access the value of the token via user.decorator.ts.
• Validates the received body via ValidatorPipe in app.pipe.ts and class-validator.
  • If the received data is not valid, the pipe throws the HTTP exception with UnprocessableEntity status code.
  • Validation rules are defined via class-validator. Check user.dto.ts.

Todo

• Better error design. UserService returns Result<T, E> where E is HttpException. And UserController just throws the errors. Is there any better design for it?
• Better strategies for tests. The test in this PR does not test whether the UserService hashes the given password before creating.
• Better validation. To validate the received body with class-validator for DTOs requires a lot of duplicated conditions. For example, the password field of UserCreateDto and UserUpdateDto should have the same validating rules, but the codes are just copied.