Open in Colab badge

[JadeMaveric]

Is your feature request related to a problem? Please describe. I've noticed several notebooks on github have an "Open in Colab" badge that let's viewers quickly setup and experiment with the code. I think this would be a super useful feature.

Describe the solution you'd like

1. Use the ColabBadge Action (repo maintainer will need to add this), and submit a PR that manually adds the {{badge}} to every existing notebook. This means that all new PRs will need to have a {{badge}} markdown cell.
2. Create a new GitHub action that automatically adds a markdown cell with the badge to the top of a new notebook.

Additional context Part of GSSoC'21