feat: add ssrSessionExists to SessionAuthForNextJS

[porcellus]

Summary of change

Add ssrSessionExists to SessionAuthForNextJS

Related issues

Test plan

• If added a new boilerplate
  • I tested the new boilerplate by running the CLI locally
  • I tested that the boilerplate is created and works correctly when using command line flags (--recipe=... for example)
• If added a new recipe, frontend or backend
  • I tested that the newly added option is usable by passing command line flags (--recipe=... for example)

Checklist for important updates

• Changelog has been updated
• Changes to the version if needed
  • In package.json
  • In package-lock.json
  • In lib/ts/version.ts
• Had run npm run build-pretty
• Had installed and ran the pre-commit hook
• If added a new recipe, I also modified types to include the new recipe in Recipe and allRecipes
• If added a new frontend, I also modified types to include the new frontend in SupportedFrontends and allFrontends if required
• If added a new backend, I also modified types to include the new backend in SupportedBackends and allBackends if required

[rishabhpoddar]

technically, the session exists here, it's just that the claims are invalid. So the prop's name ssrSessionExists doesn't fit.