feat: Update min amount for FastBTC to 0.0004

[AndonMitev]

Task: https://linear.app/liquality/issue/LIQ-111/users-reporting-sender-account-does-not-exist:

[AndonMitev]

This doesn't really behave the same way the ticket describes

In this case, min is only changed when selecting fastBTC as provider first

In the ticket, it describes the min should always be 0.0004, and that the default amount should still be liquality's min

What do we want to do?

@monokh The task were updated to pick the lowest minimum amount between multiple providers