WSTEAMA-654 Reinstate webp image support on all WS pages (pt.1)

[LilyL0u]

Resolves JIRA [https://jira.dev.bbc.co.uk/browse/WSTEAMA-652]

All images are now webp, except for when webp is unavailable it is removed by the service worker.

After discussion with @eagerterrier the decision was made to leave the picture tag because we need the home and front pages to work with fallbacks because the images can't be intercepted by the service worker on these pages. We can get rid of the fallback logic and sw logic when the iOS versions fall out of use in 6-12 months.

Do we also need to make changes to https://github.com/bbc/simorgh/blob/0ef5df7d08bb6238832c7ff76514a1214d4a057a/src/app/legacy/components/Promo/image.jsx ?

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