Find PR given commit hash #4160

Describe the feature or problem you’d like to solve

When I'm exploring a repository, I like to review the PR associated with a given commit since it will often include helpful context that doesn't make it into the commit message.

To hop from a commit hash to the associated PR, I do the following:

1. Discover an interesting commit via git log|show|blame
2. Manually open a URL like this in my browser: https://github.com/organization/repository/commits/commit-hash
3. Click the little PR link below the commit message

Proposed solution

gh pr find commit-hash

This would ideally print the PR's URL on a single line so it composes with other utilities, like open.