[BE] Guard API based on user plan

[bkdev98]

Integrate with RevenueCat to backend. https://www.revenuecat.com/docs/api-v2#tag/Overview-(v2)

Plan detail: https://github.com/get6pm/6pm/issues/132

[duongdev]

Checklist

• [x] Sync subscriber entitlements using webhook #360
• [x] API to sync all subscribers for cron job #359
• Update services to check for permission according to user's current entitlement
  • [x] Budget #362
  • [x] Wallet #363
  • [x] Category
  • [x] Transaction
  • [ ] AI transaction
  • [ ] #31
  • [ ] Get transaction list (?)