feat: client payment fields

[lissavxo]

Related to #1021

Description

Added fields param to client payment table
Changed generate payment id endpoint to add the new fields param
Added functions to update and get fields

Test plan

Test api/payments/paymentId endpoint sending an array of objects in string format called fields

Summary by CodeRabbit

• New Features

  • Add custom payment fields: create, store, retrieve, and update structured metadata on payments; schema migrated to persist fields.

• Bug Fixes / Validation

  • New validation errors and explicit responses for malformed fields, invalid field structure, and invalid amounts.

• Chores

  • Request parsing and payment creation flows updated to accept/process optional payment fields; added APIs to fetch and update those fields.

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