enhancement: add indexed parameters to ERC-6123 events for off-chain log filtering

[MASDXI]

@cfries,The current ERC-6123 interface defines trade lifecycle events containing incepted, confirmed, termination, and settled, however none of the event parameters are indexed. Adding indexed to key parameters allows off-chain systems like block explorers and event indexers to filter and search for relevant events.

// SPDX-License-Identifier: MIT
pragma solidity >=0.5.0 <0.8.0;

interface IERC6123 {

    /// ... skipping function section.
    
    event TradeIncepted(address initiator, string tradeId, string tradeData);     
    // change to `TradeIncepted(address indexed  initiator, string tradeId, string tradeData)`
    
    event TradeConfirmed(address confirmer, string tradeId);
    // change to `TradeConfirmed(address indexed confirmer, string tradeId)` 

    event TradeCanceled(address initiator, string tradeId);
    // change to `TradeCanceled(address indexed initiator, string tradeId)`

    event TradeActivated(string tradeId);
    
    event TradeTerminationRequest(address initiator, string tradeId, int256 terminationPayment, string terminationTerms);
    // change to `TradeTerminationRequest(address indexed initiator, string tradeId, int256 terminationPayment, string terminationTerms)`

    event TradeTerminationConfirmed(address confirmer, string tradeId, int256 terminationPayment, string terminationTerms);
    // change to `TradeTerminationConfirmed(address indexed confirmer, string tradeId, int256 terminationPayment, string terminationTerms)` 

    event TradeTerminationCanceled(address initiator, string tradeId, string terminationTerms);
    // change to `TradeTerminationCanceled(address indexed initiator, string tradeId, string terminationTerms)`

    event TradeTerminated(string cause);
    
    event SettlementRequested(address initiator, string tradeData, string lastSettlementData);
    // change to `SettlementRequested(address indexed initiator, string tradeData, string lastSettlementData)`

    event SettlementDetermined(address initiator, int256 settlementAmount, string settlementData);
    // change to `SettlementDetermined(address indexed initiator, int256 settlementAmount, string settlementData)`

    event SettlementTransferred(string transactionData);
    event SettlementFailed(string transactionData);
}