feat: branch support for Buddy

[srtfisher]

Adding branch support for Buddy via the BUDDY_EXECUTION_PULL_REQUEST_HEAD_BRANCH variable.

• https://buddy.works/docs/pipelines/environment-variables
• https://buddy.works/blog/changelogs/changelog-march-31-2020

[srtfisher]

@gr2m ran prettier to get it to pass if you can review.

[github-actions[bot]]

:tada: This issue has been resolved in version 11.1.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: