Anchors on the help page don't scroll correctly on first load

[louise-davies]

Description:
Anchor links within the help page work, but if we try to reload the page or click a link to a specific help heading, then the page isn't scrolled to the correct heading. I believe this is due to the headers only loading in after the browser tries to navigate to the anchor links, and so we'll need to manually scroll. A solution similar to this should work: https://ericdcobb.medium.com/scrolling-to-an-anchor-in-react-when-your-elements-are-rendered-asynchronously-8c64f77b5f34

Acceptance criteria:

• Hashes in help page url correctly scroll to the corresponding headers on page load