Introduce SoftDebtCeiling and HardDebtCeiling in ECDPs

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Where;

SoftDebtCeiling

SoftDebtCeiling can be exceeded by debt whereby the debt is above the SoftDebtCeiling. Once the SoftDebtCeiling is reached, more debt can be issued but only adhering to the SDC/SoftDebtCeiling parameters, which are:

• SDCCollateralRatio: Often greater than usual (ie. 250%);
• SDCLiquidationRatio: Often greater than usual (ie. 170%)
• SDCCollateralAsset: Can only get loans with one collateral (ie. SETR), this is always SEE in SETR Unpegged ECDP protocol;
• SDCMaxLoanAmount: The maximum amount of loan that can be borrowed to an account during the SDCPeriod;
  (The SDCPeriod is the time period when the SoftDebtCeiling in the system has been reached or exceeded.

HardDebtCeiling

HardDebtCeiling is never exceeded once it is reached, it can however also be updated to increase the HardDebtCeiling threshold.

These parameters can be used as stability mechanism triggers that help in stabilising the stablecoins during low/medium or extreme price fluctuations.

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Ref: Setheum-Labs/Setheum#934