Update endpoint to search by txHash adding chainId as optional parameter

[wainola]

Since there is the chance -small one-, that txHash could not be unique, we should fetch transfer passing txHash + chainId

Implementation details

• update current endpoint to receive chainId as optional parameter

Testing details

• update test to reflect the change

Acceptance Criteria

• tests are passing
• we are able to fetch transfer by txHash + chainId

[mpetrun5]

The issue is not with the chainID (though I guess that might be a consideration as well but hash collision is very unlikely).
The issue is that someone can program a contract that creates multiple transfers in the same transaction hash.