Add sandbox API keys, callback URL configuration, and additional payment options including currency, lifetime, fee settings, underpayment coverage, auto withdrawal, and mixed payment support to
the OxaPay provider seeder.
- Add PaymentProviderSeeder with initial provider data (Stripe, Lemon Squeezy, Polar, OxaPay, Crypto, Activation Key)
- Create migration to disable JSON constraints and change configuration column from JSON to TEXT
- Update PaymentProvider model cast from 'array' to 'encrypted:array' for secure configuration storage
