Swappers with Oracle check

[0xdcota]

An additional check can be added to swappers so that sandwich attacks are not possible or mitigated.

At the time of performing a ISwapper-swap call, the function should check if price expected is close near an external (trusted) oracle source.

Refer to implementation here

uint256 priceFromSwapper = (_collateralAmount * (10**uint256(_borrowAssetDecimals))) /
        _amountToReceive;
      uint256 priceFromOracle = _oracle.getPriceOf(
        _collateralAsset,
        _borrowAsset,
        _collateralAssetDecimals
      );
      uint256 priceDelta = priceFromSwapper > priceFromOracle
        ? priceFromSwapper - priceFromOracle
        : priceFromOracle - priceFromSwapper;

      require(
        (priceDelta * SLIPPAGE_LIMIT_DENOMINATOR) / priceFromOracle < SLIPPAGE_LIMIT_NUMERATOR,
        Errors.VL_SWAP_SLIPPAGE_LIMIT_EXCEED
      );