List contributors in both Articles and Documentation

[ZibanPirate]

When the user navigates to /Article/[article slug] here's what should happens:

• Frontend calls the endpoint: api.dzcode.io/contributors/[article slug]
• API server responses with contributors list, eg:

  {
  "contributors": [
  {
    "username": "ZibanPirate",
    "avatar_url": "https://avatars2.githubusercontent.com/u/20110076?v=4"
  },
  {
    "username": "Souhaib-Benbouzid",
    "avatar_url": "https://avatars1.githubusercontent.com/u/54677068?v=4"
  }
  ]
  }

• Frontend displays the list of contributors alongside the article, showing the user's avatar and username, and a link to his/her github profile.

[ZibanPirate]

Closing as done in #245