Test the GET request when sending a transaction request with the UI

[mcintyre94]

We can test/debug the POST request using this component: https://github.com/solana-labs/solana-pay-scaffold/blob/main/src/components/SendTransactionRequest.tsx

It sends the POST request with the connected wallet, decodes the returned transaction, logs debug information and then sends the transaction.

We should have it also send the GET request and show a helpful error if it doesn't work, since this is also required by Solana Pay and mobile wallets will error if it doesn't work correctly.