Refactor payment-methods context to be consistent with checkout-events context

[alexflorisca]

Left over work from the Feature: Data Store Migration work.

This issue is about renaming and refactoring the payment-method context to keep it consistent with the checkout-events context

• Rename the payment-methods context to payment-events
• Delete payment-method-events-context.tsx and move the code to index.tsx
• Rename some of the constants