Consider using confirmation instead of depth when validating inlucion of transactions on BTC chain

[KonradStaniec]

Currently in Babylon node, btc transactions must be at certain depth to be considered included in BTC chain. Depth is defined as number of block which bury given transaction, so transaction in the tip block will have depth equal to 0, in the next after tip 1.

In BTC world, more popular is counting number of confirmations. Transactions in tip block is considered to have 1 confirmation.

Given that confirmations are more popular than depth, it make sense to start using it on Babylon node.