Fix deploy button in with-xata example

[SferaDev]

The deploy button of the with-xata example is not working properly because we were lacking the integration to configure the env variables.

Taking advantage of the PR, some other changes:

• Adding alt to next/image to fix build with latest version
• Update readme to add more information in the Xata CLI section
• Use a new command to initialize the database schema on first deployment
• Remove hardcoded URL in xata.codegen.ts
• Remove deprecated formatVersion in schema.template.json
• Update dependencies

Note: The integration is still work in progress, it works for the Deploy to Vercel button but we want to improve the UI/UX before submitting it to the Marketplace, keeping it unlisted for a while.

cc: @atilafassina