Provide the balance dynamically for Confirm (issue 401)

[Yonben]

It seems to be the only thing, but I don't know your codebase like you do ;) Let me now if anything else is needed.

It's a fix for #401 :)

[cstenglein]

Thank you very much! Will look into it in the coming days :)

[escapedcat]

If possible would be nice to add a test for this here: https://github.com/Yonben/raspiblitz-web/blob/ISSUE-401-confirm-modal-fix/src/pages/Home/SendModal/__tests__/SendModal.test.tsx

[Yonben]

@escapedcat I added tests, thanks for highlighting that :)
@cstenglein I'm not sure I understand why the ConfirmSendModal uses both amount and invoiceAmount. The former isn't used at all but invoiceAmount is just a reference to amount. Since it supports both invoices and onchain, it seems the more generic name amount is a better fit here.

What do you think?

[cstenglein]

@Yonben yeah, looks like I started it sometime but didn't finish it. Just using amount would be the better idea here.

Anyways, the PR looks good & you even wrote tests, thank you very much 👍