Create users summary endpoint

[ThukuWakogi]

Create an endpoint through which we one can get a summary on users Add data to JobGrade as provided in the Competency Evaluation Framework and add jobgrades to several users using the data generated give a summary of the users indicating the total amount of users plus the number of users per job grade The endpoint should return a json in the following format

{
    "total_number_of_user": 132,
    "champions": 11,
    "Experts": 22,
    "Practitioners": 35,
    "Beginners": 64
}

The endpoint url should be /api/users/summary/