Because it was useful in soap (addSelectBoxFieldValues)

Add a new route

OPTION|PATCH /trackers_fields/:id
{
    "new_values": [
        "valueA", "valueB", ...
    ]
}

Limitations

• This route can only be used by tracker administrators and upper (project admin, etc)
• It only works on tracker that are active in active projects
• It only works on "selectbox" like fields (selectbox, multi-select box, radio, checkboxes)
• It only works on list fields bound to static list of values
• It can only add new values (without color decorators)