Fix regtest for some functions

[Polybius93]

Some functions doesn't work with regtest networks, where this function is being used:

bitcoinNetworkModeToCoreNetworkMode

This function converts the regtest network type to testnet, which makes the regtest address not compatible.

For example:

• sending BTC to a regtest address is not working, error is:

Address is for incorrect network

[kyranjamie]

When fixing this bug, let's write an automated test that sets the network to regtest, and ensures the bitcoin sending flow works (will require API mocks)

[pete-watters]

A pre-cursor to this task is to setup the environment https://github.com/leather-io/issues/issues/159