[16] [Backend] Add User service

[markgravity]

https://github.com/markgravity/flutter-survey/issues/16

What happened

We need a service to handle API calls relate to User

Proof Of Work

flutter: *** Request ***
flutter: uri: https://nimble-survey-web-staging.herokuapp.com/api/v1/me
flutter: method: GET
flutter: responseType: ResponseType.json
flutter: followRedirects: true
flutter: connectTimeout: 0
flutter: sendTimeout: 0
flutter: receiveTimeout: 0
flutter: receiveDataWhenStatusError: true
flutter: extra: {}
flutter: headers:
flutter:  authorization: Bearer i6LRD9fqvn6UGY_lFhJG2uIJktMVd8AW7T8BEiZkRRk
flutter: data:
flutter: null
flutter:
flutter: *** Response ***
flutter: uri: https://nimble-survey-web-staging.herokuapp.com/api/v1/me
flutter: statusCode: 200
flutter: headers:
flutter:  connection: keep-alive
flutter:  cache-control: max-age=0, private, must-revalidate
flutter:  transfer-encoding: chunked
flutter:  date: Wed, 05 May 2021 16:47:54 GMT
flutter:  vary: Accept-Encoding, Origin
flutter:  content-encoding: gzip
flutter:  strict-transport-security: max-age=31536000; includeSubDomains
flutter:  referrer-policy: strict-origin-when-cross-origin
flutter:  x-permitted-cross-domain-policies: none
flutter:  content-type: application/json; charset=utf-8
flutter:  x-xss-protection: 1; mode=block
flutter:  server: Cowboy
flutter:  x-request-id: 54523b47-beb2-4498-9403-2dd826ef6478
flutter:  x-download-options: noopen
flutter:  x-runtime: 0.033422
flutter:  etag: W/"1a245fba319b70e0b337c99eb6c83ecb"
flutter:  via: 1.1 vegur
flutter:  x-frame-options: SAMEORIGIN
flutter:  x-content-type-options: nosniff
flutter: Response Text:
flutter: {"data":{"id":"2","type":"user","attributes":{"email":"dev@nimblehq.co","avatar_url":"https://api.adorable.io/avatar/dev@nimblehq.co"}}}

[sleepylee]

please update your POW to the PR as per our normal workflow, PR template. 🙇