Conch should have an OpenSSH-compatible client configuration parser

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i.e. we should be able to parse ~/.ssh/config and /etc/ssh/config files and support the various features which they support.

This ticket should be resolved when the basic infrastructure for such a thing is in place; for example, there are features (like X11 forwarding) which would require substantial additional effort to implement the feature rather than just the configuration for that feature, and we shouldn't block on that.

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This depends on #3829 being implemented first, so there's some backend to feed the configuration data to.