[Guidance]: Missing sub-headings in page headers on certain pages

[GCHQ-Developer-112]

Summary

Most of the page headers used on the site have a sub-heading also to describe the page. However, there are some pages that only have a heading

💬 Description

Examples of pages that have no sub-headings are:

• Colour
• Icons
• Motion
• Elevation
• Typography
• Focus Indicator

💰 Use value

This improvement will create more consistency on the guidance site whilst also providing extra context on what the page is about.

Raised by: @GCHQ-Developer-465 & @MI6-255

[mi6-577]

Colour has been changed in v3 and now includes a subheading, the others remain without subheading