feat: add spent amounts to POST /outgoing-payment

[BlairCurrey]

Changes proposed in this pull request

• adds grantSpentDebitAmount and grantSpentReceiveAmount to outgoing payment create response
• adds "Web Monetization" example to Bruno collection

Context

https://github.com/interledger/rafiki/issues/2678

Checklist

• [x] Related issues linked using fixes #number
• [x] Tests added/updated
• [ ] Documentation added
• [x] Make sure that all checks pass
• [x] Bruno collection updated

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