[fix] Send correct error message from TX preview failure

[matiasbzurovski]

Changelog

• If the transaction analysis fails with FailedTransactionPreview, we should send back the error message that Sargon determines (instead of "Unknown reason").
• Stop appending ET failed to generate TX review before any error parsed during TX preview loading.
• If the error is an unknown CommonError (meaning a specific message cannot be determined for it for this flow), include its code in the message sent back to the dApp.
• Updates error messages to be more descriptive

Before vs After

Before

"message": "ET failed to generate TX review: Failed to retrive TX receipt from gateway: Unknown reason"
"message": "ET failed to generate TX review: Transaction Manifest contains forbidden instructions"

After

"message": "Error when generating TX preview: Unknown reason, code: 10093"
"message": "Transaction Manifest contains forbidden instructions"  

Before	After

[CyonAlexRDX]

LGTM