Add Support for Todos API Endpoint

[Ichirobtw]

It appears that the GitLab API client for PHP does not currently support the GitLab Todos API endpoint. This endpoint provides functionality for managing to-do items, which is essential for integrating tasks and notifications from GitLab.

Expected Behavior:
The client should offer methods to interact with the following key functionalities of the Todos API:

• List todos
• Mark a todo as done
• Get a specific todo

Actual Behavior:
Currently, there is no direct support for interacting with the Todos API. It would be helpful to have built-in methods for:

• Fetching a list of todos (GET /todos)
• Marking todos as done (POST /todos/:id/mark_as_done)
• Viewing individual todos

Feature Request:
Please consider adding support for the following endpoints:

• GET /todos - Fetch a list of todos assigned to the authenticated user.
• POST /todos/
• /mark_as_done - Mark a todo as done.
• GET /todos/
• Retrieve details of a specific todo.

Benefits:
Adding support for the Todos API would enhance the client's usefulness for developers managing tasks and notifications within GitLab, allowing for more comprehensive project management and automation within PHP applications.

Relevant Documentation:
GitLab Todos API Documentation