Configurable flat reward in operator triggered settlement challenge

[jijordre]

Description

In the event that operator triggers a driip settlement challenge or null settlement challenge a component in the challenger's reward will be a flat fee consisting of configurable amount and currency.

The foreseen work can be decomposed as follows:

• Add reward amount and currency in Configuration.
• Add support for flat monetary amount reward in SecurityBond. (Now it only supports fractional reward.)
• Update reward schemes in DriipSettlementDispute.
• Update reward schemes in NullSettlementDispute.

Definition of done

• Targeted contracts have been updated
• Unit tests have been updated

Details & Questions

Depends on

[jijordre]

Closed by #301.