feat(ui): add a scroll to top button

[a2937]

Checklist:

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)

Closes #634

It would be great if I could manage to make a test to ensure it's position is sticky, but this should be suitable enough for now.

[scissorsneedfoodtoo]

Hi @a2937, thank you for your patience, and for all your hard work on this. This is off to a great start.

I'm getting some feedback from Quincy and others about whether we want to add a "Scroll to top" button or not, and if so, what sort of behavior and placement it should have.

Once I hear from everyone I can circle back and take another look at your PR.

[scissorsneedfoodtoo]

Hi @a2937, thank you again for all of your hard work on this feature.

After talking with Quincy and the rest of the team, and seeing how most other tech blogs don't have a scroll to top button, we decided not to add this feature in for now.

Still, we'll listen for feedback from our readers, and if a lot of people ask for this we have a good start with your PR here.

As always, thank you for everything you're doing for the freeCodeCamp community.