Implement Mercure hook

[vincentchalamon]

• Mercure hook: https://github.com/api-platform/demo/blob/main/pwa/utils/mercure.ts
• HubURL from: https://github.com/api-platform/demo/blob/main/pwa/utils/dataAccess.ts#L14-L23 and https://github.com/api-platform/demo/blob/main/pwa/utils/dataAccess.ts#L41-L44
• Usage: https://github.com/api-platform/demo/blob/main/pwa/pages/books/%5Bid%5D/index.tsx

[artandor]

Looks very simple and nice to implement ! Hope it'll be merged soon