Grants detail page - make it better

[Tymmmy]

We need to make a human readable string from the grant interval - Grants detail page when having a web monetization grant

https://github.com/tolu/ISO8601-duration?tab=readme-ov-file#example https://en.wikipedia.org/wiki/ISO_8601#Repeating_intervals We will probably need to parse this ourselves (maybe another library in the open-payments repo?)