Reduce Bitcoin dust threshold to avoid dropped user outbounds

Outbounds below the dust threshold are swallowed. While the 10k sat threshold was reasonable at lower Bitcoin prices, at the current value it results in all BTC outbounds less than $10 being dropped. There may be some edge cases to consider so the code base should have a quick audit when updating the value at https://gitlab.com/thorchain/thornode/-/blob/develop/common/chain.go?ref_type=heads#L275.