A reviewer must provide a reason when rejecting a push 💬

[JamieSlome]

Is your feature request related to a problem? Please describe.

When a reviewer rejects a push, either through the UI or API, it is unclear why the push has been rejected. This makes it difficult for the developer to understand what changes need to be made and requires further friction to resolve the issue.

Describe the solution you'd like A clear and concise description of what you want to happen.

Enforce a custom text input for a rejection reason when rejecting a push. As we look to automate GitProxy further, this will also come in handy when we auto-reject pushes as we will need a description and information about why a push was auto-rejected.