#163478804 Implement user followership

[jsamchineme]

What does this PR do?

Implement user followership

Description of Task to be completed?

• write unit tests for the endpoints
• protect the route with passport middleware
• implement the controller logic

How should this be manually tested?

• clone this branch feature/163478804/user-followership
• signup two users with the POST /api/users endpoint
• get the userId of user1 and the token of user2
• get user2 to follow user1 using the endpoint POST /api/users/{user1Id}/follow
• check that the id of user2 is present in the array of followers returned in the response.data.followers property.
  NB: response.data refers to the user who is being followed whose id is passed in the request /api/users/{user1Id}/follow

Any background context you want to provide?

None

What are the relevant pivotal tracker stories?

https://www.pivotaltracker.com/story/show/163478804

Screenshots (if appropriate)

None

Questions:

None