[feature]: support multiple ZMQ topics on same socket

[jblachly]

Is your feature request related to a problem? Please describe.

bitcoind supports using the same port / PUB socket for greater than 1 type of ZMQ topic:

https://github.com/bitcoin/bitcoin/blob/master/doc/zmq.md

However, LND does not support this:

failed to load config: ValidateConfig: unable to load RPC credentials for bitcoind: zmqpubrawblock and zmqpubrawtx must be set to different addresses

Describe the solution you'd like

It would be great if LND could support this to minimize the number of distinct port numbers needing to be tracked

Describe alternatives you've considered

Obviously using separate ports

Additional context

[sputn1ck]

This will require some changes to https://github.com/btcsuite/btcwallet/ , I can have a look if I have some spare time.

[saubyk]

moving this to a discussion under Ideas