feat: Review Channel Purchase - add fiat display

[bjorn]

When opening a channel on Alby Hub, there is no fiat estimate displayed once you reach the Buy Channel page:

No fiat estimate included.

This seems like an odd omission because virtually all other locations where a value is displayed we see both Bitcoin and fiat value. Suggested solution (numbers not accurate):

Display of fiat values (mock-up).

(I'm not sure about the ~ character, it's not used in most places, though it was used on the "Open Channel with Lightning" page where I copied the values used in the mock-up from)

[rolznz]

I agree, thanks for creating the issue! And I think the title should be "Review Channel Purchase". I've added it to our next release milestone.