tendermint-proxy: 🤝 https connections only last for one request

[cratelyn]

our TendermintProxyService implementation creates a new HttpClient to handle each specific request. if we are communicating via https, this entails a more involved handshake to establish a connection. an optimization to consider at some point would be holding a client somewhere more durable, so that we don't need to do that work for every single request we service.