Apply minimum payment-thresholds (and scan-intervals) in the codebase

[kauri-hero]

Implement and enforce "minimum values" for rate-pack and debt-thresholds, to ensure it cannot be set to unrealistic amounts.

Discussion of the aspects of the payments curve and constraints:

• consider payables payments not requiring a maturity threshold (essentially pay as soon as any payable debt reaches the threshold)
• separate the thresholds (for time and payments) for payables and receivables to be more customized for each side of the demand-supply of the network

Extra Considerations:

• consider the relation between scan intervals and the debt-threshold time amounts

CC: @czarte @bertllll

[kauri-hero]

We will need to have in-depth discussion with you @dnwiebe to try to elaborate more on the design decisions around the current payment curve and how the parameters were related to eachother