Add buttons for common actions in the Playground

In [Kubernetes#k14s](https://kubernetes.slack.com/archives/CH8KCCKA5/p1595561897223900) Slack, @ggolin put forth:
> may i make a small suggestion for the getting-started page: "select-all+copy-to-clipboard" button, "back-to-top" button, "collapse file" button.

Start by locating the Playground and its getting-started page mentioned in the issue. Check how the page currently handles file selection, scrolling, and file collapsing; done means the page provides buttons for select-all and copy-to-clipboard, back-to-top, and collapse-file actions.

Written by the indexing model from the issue text.