Add `marina.broadcastTransaction`

[tiero]

User can find this API useful to let Marina handle pushing tx to the network and eventually credit virtual change output if recognized

[bordalix]

@tiero, let me see if I correctly understood this: the idea is to have this function exposed in the marina provider API, is that it?

[tiero]

I think this function should do a) push transaction to explorer (yes doing what you linked b) scan for known change outputs like we do in sendTransaction and add a virtual utxo