Allow hostname RPC support

[Anyitechs]

This splits the rpc_address configuration field into two fields, rpc_host and rpc_port to allow hostname support, especially in containerized environments.

Closes #66

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[tankyleo]

Up to you people to make the call, I'd prefer parsing a single <hostname>:<port> string rather than splitting that setting into two parameters. This is what I do in VSS, it optimizes for fewer config params. That setting is logically a single thing right?

[Anyitechs]

That setting is logically a single thing right?

I agree it is. The problem was that we parse this setting using SocketAddr and that has a limitation of only supporting IP addresses. In containerized environments where the IP address might change if the container restarts, the user will have to update this setting each time it restarts. But supporting hostname simplifies things, because you only have to map the setting to a hostname and not worry if/when the IP changes.

An alternative to using SocketAddr (without splitting) is the ToSocketAddrs trait which supports hostname but it's sync and blocking.

UPDATE:

Missed "I'd prefer parsing a single <hostname>:<port>" from the comment earlier. Will drop the split.