Create tests for all resources

[dariusc93]

Implement tests for every resource with an environment variable holding the stripe key.
This should be able to replace the examples.

• Coupons
• Credit Notes
• Discounts
• Invoice Items
• Invoices
• Plans
• Subscription Schedules
• Subscriptions
• Tax Rate
• Usage Records
• Checkout Sessions
• Account
• Application Fees
• Application Fees Refund
• Country
• External
• Persons
• Topup
• Transfer Reversal
• Transfer
• Balance
• Charges
• Customer
• Customer Tax ID
• Disputes
• Events
• File
• File Link
• Payment Intents
• Payout
• Product
• Refunds
• Token
• Review
• Value List Items
• Value Lists
• Authorizations
• Card Holders
• Cards (Issuing Card)
• Dispute (Issuing Dispute)
• Transactions
• Order
• Returns
• SKU
• Bank
• Cards
• Payment Methods
• Source
• Sigma
• Connection Tokens
• Locations
• Readers
• Webhooks