Use Case K13: Reset / release external charging limit about libocpp

[Giavotto]

Scenario

1. External control system release/removes a charging limit/schedule on the Charging Station
2. When a transaction is ongoing, the Charging Station calculates the new Charging Schedule and
   adjusts charging speed.
3. The Charging Station sends a ClearedChargingLimitRequest to notify the CSMS.
4. The CSMS acknowledges with a ClearedChargingLimitResponse to the Charging Station.
5. When the change has impact on an ongoing charging transaction and is more than:
   LimitChangeSignificance, the Charging Station sends a TransactionEventRequest to notify
   the CSMS.
6. The CSMS acknowledges with a TransactionEventResponse to the Charging Station.

Functional Requirements

• K13.FR.01: A transaction is ongoing AND External charging limit is released/removed, the Charging Station SHALL NOT limit charging anymore based on the previously received limit.
• K13.FR.02: When K13.FR.01, the Charging Station SHALL notify the CSMS by sending a ClearedChargingLimitRequest message.
• K13.FR.03 K13.FR.01 AND Charging rate changed by more than: LimitChangeSignificance, the Charging Station SHALL send a TransactionEventRequest message to the CSMS with trigger = ChargingRateChanged.