Extend transaction request to support the value of ethereum transaction `data` field directly.

In the current Transaction Manager API, it exposes most of the ethereum transaction fields apart from the input data: https://github.com/hyperledger/firefly-transaction-manager/blob/main/pkg/ffcapi/api.go#L231. the input data is constructed using the method and params inside the transaction manager logic. While this design satisfies the need of Firefly functionality, it creates friction for web3 developers to try out the Transaction Manager API with the raw eth transaction payload.

Therefore, to improve the flexibility of transaction manager, `data` fields should be added to the existing input transaction fields as an alternative to the existing fields.

Start with the Transaction Manager API definition in pkg/ffcapi/api.go at the linked transaction input fields, then trace how method and params are processed. Confirm the expected raw Ethereum data representation and identify the relevant transaction handling tests. Done means the data field is accepted as an alternative to the existing method and params input.

Written by the indexing model from the issue text.