Sync assignees to GitHub

[joshsmith]

Problem

When a task is assigned a user on Code Corps, we need to be able to sync that assignee to GitHub.

[joshsmith]

When assigning:

• In the UserTaskController create or update
• Check if the task has a github_issue
• Check the assignee can be assigned using GET /repos/:owner/:repo/assignees/:assignee
  • 204 response if yes
  • 404 response if no
• then POST /repos/:owner/:repo/issues/:number/assignees with a key of "assignees" and value of an array of GitHub usernames

When unassigning:

• In the UserTaskController update or delete
• Check if the task has a github_issue
• Check the assignee can be assigned using GET /repos/:owner/:repo/assignees/:assignee
  • 204 response if yes
  • 404 response if no
• DELETE /repos/:owner/:repo/issues/:number/assignees with a key of "assignees" and value of an array of GitHub usernames