Activity: 'fee' is lower case hardcoded ->not ok for all languages

[myxmaster]

This is not working for some languages (e.g. German), since lowercase is a clear spelling mistake for the word "fee".

https://github.com/ZeusLN/zeus/blob/1ab82d35a0d44d0e5becc937bb03987776edda26/components/Amount.tsx#L120-L123

I don't have a better idea than making a new locale string for this, so it can be individually decided for each language.