chore(backend): allow asset scale 2 to asset scale 9 payments

[mkurapov]

Changes proposed in this pull request

• Fix issue where we are unable to send payments between asset scale 2 and asset scale 9 wallet addresses because the ILP rate probe exchange rate numerators were too big to store in the DB as bigints. See details in issue.
• Update small logic where we allow fees to make up more than 50% of receive amount: https://github.com/interledger/rafiki/pull/2748/files#r1616401580
• Some minor error/logging additions, refactoring create quote function slightly

Context

Fixes #2747

Checklist

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

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