Allow user to choose bitcoin unit

[yashrajd]

I just noticed that Cake doesn't allow users to choose bitcoin units at all.

This is a hygiene feature that's offered by most wallets out there, letting users choose between bits, sats & what not. It's also a strict UX improvement IMO since small bitcoin amounts are hard to read or write.

I recently ran into this issue where I mistakenly entered one less 0 than I wanted to, and was about to send 10x the bitcoin than I intended. Please add this optionality for us users.

My personal preference is for BIP 177 with ₿ & BTC (for 100M base units), but primarily I just want to optionality. What do you think?