AV-Embeds Next.js routing

[amoore108]

Part of https://jira.dev.bbc.co.uk/browse/WSTEAM1-1191

Overall changes

• Adds routing to handle av-embeds routes in the Next.js app and a basic debug output
• Moves ThemeProvider out of PageWrapper and into withContexts and _app, beside the other Context providers. This is required as the av-embeds routes do not need to render the page furniture (header/footer etc) that PageWrapper provides, but should still be able to produce a correctly styled 404/500 page if an incorrect route is provided

Code changes

• Adds handling of the av-embeds route in the [service]/[[...]].page.tsx catch-all
• Adds parsing logic to extract values from requested URL to allow data fetching for media content
• Adds boilerplate for AV_EMBEDS analytics
• Moves ThemeProvider out of PageWrapper and into withContexts for the Express app and _app for the Next.js app
• Updates Storybook stories that need more granular ThemeProvider control

Testing

1. Run branch locally
2. Visit: http://localhost:7081/serbian/cyr/av-embeds/srbija-68707945
3. Check it parses the URL and returns an object with the expected values
4. Visit: http://localhost:7081/russian/av-embeds/features-49881797/pid/p07q3wwl
5. Check it parses the URL and returns an object with the expected values
6. Visit: http://localhost:7081/serbian/cyr/av-embed/srbija-50103048/pid/p07rfhrv
7. Check it returns a 404 page (note the missing s in av-embeds in the URL)

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