Feature: Implement Get User Details API (GET /api/users/:userId)

[MessiasLima]

Feature: Implement Get User Details API (GET /api/users/:userId)

Background

This feature involves implementing the GET /api/users/:userId endpoint from the Umami API within the umami-kotlin library. This endpoint allows an authenticated user to retrieve detailed information about a specific user by their ID. This is essential for displaying user profiles, managing user-specific settings, or integrating with other user-centric features.

Implementing this functionality is crucial for providing comprehensive user management capabilities within the umami-kotlin client. It will enable applications to fetch and display individual user data, contributing to a more complete and interactive user experience. This work directly contributes to fulfilling the "Umami API" section of the project roadmap.

Acceptance criteria

• GIVEN the Umami client is configured with a valid baseUrl and an authenticated user,
  WHEN a request is made to get details for a valid userId via a new API method (e.g., umami.users.getUser(userId)),
  THEN the client successfully sends a GET request to /api/users/:userId
  AND the method returns a successful response containing the user's details.
• GIVEN the Umami client is configured with a valid baseUrl and an authenticated user,
  WHEN a request is made to get details for an invalid or non-existent userId via the new API method,
  THEN the client successfully sends a GET request to /api/users/:userId
  AND the method returns an error response (or throws an appropriate UmamiNotFoundException) indicating the user was not found.
• GIVEN the Umami client is configured with a valid baseUrl,
  WHEN a request is made to get user details by an unauthenticated user via the new API method,
  THEN the client successfully sends a GET request to /api/users/:userId
  AND the method returns an error response (or throws an appropriate UmamiAuthException) indicating insufficient privileges.
• GIVEN the Umami client is configured,
  WHEN a request is made to get user details and a network or server error occurs during the API call,
  THEN the new API method throws an appropriate exception (e.g., IOException, UmamiApiException).
• GIVEN the umami-kotlin library is used in a project,
  WHEN a developer initializes the Umami client using Umami.create(),
  THEN the Umami instance exposes a public method (e.g., umami.users.getUser(userId: String): User) to interact with the GET /api/users/:userId endpoint.