Market data API: Add unique trade identifiers to the "/api/trades" responses

[unbeaten69]

The responses provided by the https://markets.bisq.services/api/trades endpoint do not contain any trade identifiers at the moment. Having them, similarly to how the https://markets.bisq.services/api/offers endpoint provides them, often makes API consumption a bit easier.

It's a low priority thing though as the responses also contain high precision trade timestamps which can easily be used as trade identifiers by API clients.