Consolidate and update button and link styles, including hover states

[j-jaworski]

@j-jaworski completed a full audit of link and button styles across the site and cardigan and defined styles for:

1. Primary buttons (colour 1)
2. Secondary buttons (colour 2)
3. Tertiary buttons (outline), including white
4. Text links, including white

• Icons - placement, size and spacing across all types
• States - Default, hover, active (click/tap) and focus states across all types
• Responsive sizes (font size and spacing aligned with cardigan) across all types

Focus states have been "inspired" by Gov.uk design system, and take a high contrast approach to work best for the users who need to rely on focus states to navigate.

Designs on Figma Link to Figma Screenshot for reference:

[j-jaworski]

This work covers the following previous tickets Determine link behaviour in order to align across platform #9791 Improve colour contrast on cookie banner with keyboard focus #10243