CheckRun - Add ability to get the head sha + Implement GH Status Event

[avano]

Description

• CheckRun - Add ability to get the sha of the related commit
• Status - Add class representing GH Status Event

Before submitting a PR:

We love getting PRs, but we hate asking people for the same basic changes every time.

• Push your changes to a branch other than master. Create your PR from that branch.
• Add JavaDocs and other comments
• Write tests that run and pass in CI. See CONTRIBUTING.md for details on how to capture snapshot data.
• Run mvn -D enable-ci clean install site locally. This may reformat your code, commit those changes. If this command doesn't succeed, your change will not pass CI.