Provide assignable users for project
        :param project_key:
        :param start: OPTIONAL: The start point of the collection to return. Default: 0.
        :param limit: OPTIONAL: The limit of the number of users to return, this may be restricted by
                fixed system limits. Default by built-in method: 50
        :return:

def get_all_assignable_users_for_project(self, project_key, start=0, limit=50):
        """
        Provide assignable users for project
        :param project_key:
        :param start: OPTIONAL: The start point of the collection to return. Default: 0.
        :param limit: OPTIONAL: The limit of the number of users to return, this may be restricted by
                fixed system limits. Default by built-in method: 50
        :return:
        """
        url = 'rest/api/2/user/assignable/search?project={project_key}&startAt={start}&maxResults={limit}'.format(
            project_key=project_key,
            start=start,
            limit=limit)
        return self.get(url)