Add "Scroll To Top" button on mobile and/or desktop to the Docs page

[TisVictress]

In the Figma design document, there is an example of a "Scroll To Top" button that may enhance usability on a mobile device. Let's add this for the Paketo docs page.

It may also be helpful to add this button for Desktop users but I cannot find this usage in the Figma design doc.

We should determine the best position(s) for this button. For example, a scroll-to-top button can exist at the bottom of the docs page (a single button). Alternatively, one can exist for each section near section headers (multiple buttons).