Feat: add fiat denominated withdraw links

[talvasconcelos]

Closes #44

[dni]

on pay_links, this is solbed by using.

    # database only allows int4 entries for min and max. For fiat currencies,
    # we multiply by data.fiat_base_multiplier (usually 100) to save the value in cents.
    if data.currency and data.fiat_base_multiplier:
        data.min *= data.fiat_base_multiplier
        data.max *= data.fiat_base_multiplier```

[talvasconcelos]

on pay_links, this is solbed by using.

    # database only allows int4 entries for min and max. For fiat currencies,
    # we multiply by data.fiat_base_multiplier (usually 100) to save the value in cents.
    if data.currency and data.fiat_base_multiplier:
        data.min *= data.fiat_base_multiplier
        data.max *= data.fiat_base_multiplier```

there's no fiat multiplier here!

[talvasconcelos]

can I merge this one @dni ?