GitHub service objects for getting an issue or PR based on its URL

[hpjaj]

Background

There will be times when a user needs to manually add in an issue or pull request into their week in review, that is not showing up already.

If it does not already exist in our db, we'll need to fetch it from GitHub's API.

Definition of Done

• GitHub service object to find an issue based on its HTML URL
• GitHub service object to find a PR based on its HTML URL

[hpjaj]

completed