Adding 3 new features to extension

[leesalminen]

This PR adds 3 new features to Boltcards extension:

1. Card expiration date - you can now set a YYYY-MM-DD expiration date for a card and it will not allow withdrawals after that date.
2. Monthly spend limit - you can now set a monthly spend limit for a card and it will not allow withdrawals above that amount in a given calendar month
3. Limit type - you can now choose to track daily & monthly limits in fiat. This leverages the fiat tracking functionality in core and must be enabled to function properly.

Can use/try this update from Bitcoin Jungle's lnbits extensions repo: https://raw.githubusercontent.com/Bitcoin-Jungle/lnbits-extensions/main/extensions.json

[leesalminen]

Hey - just checking in on this. Are you open to accepting this PR?

[arbadacarbaYK]

tested the version on the bitcoin jungle instance, works perfect. @dni

[prusnak]

shouldn't the limit_type be some kind of an enum?

https://docs.pydantic.dev/1.10/usage/types/#enums-and-choices