Integrate CIFlow

[driazati]

Currently probot adds a comment (example to all (non opted-out) PyTorch PRs with information about CIFlow. We should integrate this into the PR HUD and use the authorization token that we already have to control the labels on a PR. In order, we can:

• implement the same view as the comment but with click-to-add-a-label functionality as its own React component
• compress the view with some interactive features
• answer questions like: what labels do I need to add X jobs