js sdk: getProposeTransaction could take txBuilder instance as txData

### Is your feature request related to a problem?

The function `getProposeTransaction` takes an object as txData. It forces the developer to know which fields this object should have.
It is another way to create a transaction than the usual way using the transactionBuilder from the archethic SDK.

### Describe the solution you'd like

Instead of a new object, the txData could be an instance of the TransactionBuilder from the archethic SDK. This could simplify the creation of the transaction as the developer will use the usual creation of transaction with the txBuilder functions.
Then the multisig SDK could retrieve the fields from the TransactionBuilder instance and format it as the multisig contract needs.
So the multisig format would be transparent for the developer

### Additional context

_No response_

### Epic

_No response_

Locate the getProposeTransaction entry point and inspect how its txData object is currently formatted for the multisig contract. Compare that path with the Archethic SDK TransactionBuilder usage described in the issue. Done means callers can pass a TransactionBuilder instance while the multisig format remains transparent to them.

Written by the indexing model from the issue text.