[ic-footer] Retro-fit ic-accordion-group

## Summary
ic-footer with grouped links currently has a custom accordion like design pattern. Retrofitting to use an ic-accordion-group would give developers more control over the grouped links and bring more a11y to the component (ie, focus states, animation.

## 💬 Description
Ticket will have to go through Design to have ic-accordion work on a coloured background.

Start at the ic-footer component and inspect the existing grouped-links accordion pattern alongside ic-accordion-group. Confirm the Design decision for using ic-accordion on a coloured background, then verify that grouped links use the shared component with its focus and animation behaviour.

Written by the indexing model from the issue text.