BACKEND - Implement getCohortByUserId #106

What

• Frontend needs an efficient way to get the cohort for the currently logged in user.

TO DO

• Implement a getCohortByUserId endpoint which retrieves the latest cohort the user has been added to.
  • Example: localhost:port/cohorts/userId/{userid}

Acceptance Criteria

• Response from the endpoint should return the following as the data object:

"id": 1,
    "title": "Cohort 1",
    "courses": [
      {
        "id": 1
        "title": "Software Development",
        "students": [ ],
        "teachers": [ ]
      }
    ]