New endpoints and bugfixes

Introduced the GET /tasks endpoint, enabling the retrieval of a list of tasks.
Introduced the POST /fields/{id}/choices endpoint, allowing the addition of new choices to a field.
Corrected the example of the color field in the response of the GET /fields endpoint.
Clarified that the color field is supported exclusively for fields of type label.
Removed the color field from the response of the POST /fields/{id}/choices endpoint.