Transfers exchange rate further improvements

Thanks to https://budgetflow.featurebase.app/submissions/64f9802345d694dae55060b1

we can change the currency exchange rate for a transaction.

However, a significant improvement for quality of life would be the ability to set the exchange rate in the window where we input the transfer data.

The creator could discern when we're making a transfer from, let's say, USD to EUR, and show the exchange rate there, along with the option to adjust it as needed.

This change would make transfers between different currencies more user-friendly with less work to do afterwards.

Suggesting this, cause even tho the exchange rate is updated often in the app, banks are applying their fees during the exchange, and that rate will almost always be different.