Update the simulateTransaction response

[L-Zuluaga]

ℹ️ This issue is part of Epic #158

Objective

It’s required to update the simulateTransaction response in the soroban.ex repo, in order to implement in the result the stateChanges . The info about the endpoint specification can be found in the stellar documentation:
https://github.com/kommitters/soroban.ex/blob/main/lib/rpc/responses/simulate_transaction_response.ex
stellar/js-stellar-sdk#936

Checklist

• Update the response of the simulateTransaction
• Add and update the respective tests
• Update the readme