PRP-6052: Add btc_markets_connector

This PR adds a connector for the btcmarkets.net exchange: https://www.btcmarkets.net/

Since founding in 2013, BTC Markets is one of the largest, most liquid cryptocurrency exchanges in Australia.

This connector was previously approved in

https://snapshot.org/#/hbot-prp.eth/proposal/0x352f5bb7ff863628edf636af30d8e641b020fb7d61a902d0d8def3a430d054b6

https://snapshot.org/#/hbot-prp.eth/proposal/0x5f90e1b77c8c7f1c6a8cfbc6591aae78b76cbe1663d8954e1c090e10299b08e8

and only got merged in on 29/11/2022 as part of https://docs.hummingbot.org/release-notes/1.10.0/ however it didn't receive enough votes during Epoch 3 Polls - https://blog.hummingbot.org/epoch-3-and was removed on 27/01/2023 in https://docs.hummingbot.org/release-notes/1.12.0/

There was limited time to source support for the BTC Markets connector, particularly considering the holiday period. BTCMarkets are excited about the connector and envisage creating a community with their existing traders and ‘skill up’ other customers in the wonderful world of automated trading, thereby gathering further support and interests to the Hummingbot community.