Investigate what changes to make for using the new Service Navigation component

[romaricpascal]

What

Investigate and build a spike of changes we'd need to make for using the new Service Navigation component. The aim is to understand if possible to use the new component considering the bespoke feature the Design System site has, especially:

• what to do with the search bar, currently in our custom header
• distinguishing between a navigation item representing the current page itself or a parent of the current page, which we don't do at the moment
• how to do with our current navigation which offers two levels on mobile, with accordion for expanding/collapsing

Why

Now we've released a new component to help users navigate, it'd be great to use it for our own site, unless our bespoke features prevent us to.

Who needs to work on this

Developers, mostly, but designer/content folks will likely need to be involved when looking at the mobile navigation

Who needs to review this

Developers, mostly, but designer/content folks will likely need to be involved when looking at the mobile navigation

Done when

We've documented either:

• [ ] The changes we could tidily implement to use the Service Navigation component
• [ ] What's preventing us to use the Service Navigation component at the moment

[CharlotteDowns]

Also tracked by Update Design System website to use Service navigation component #4239