refactor: use descriptive verbs for SSH config construction

[th3james]

Changes

I noticed that ssh.NewConfig has a stateful side effect (exec'ing ssh) and discarded its errors. Because stateful calls are so critical for performance and reliability, I prefer it when function names make it clear that they are stateful, which, IMHO NewConfig does not. I recognise this may go slightly against the conventions for the use of New for constructors in this repo, so happy to debate this.

• Renames: ssh.NewConfig -> ssh.LoadConfig
• Renames: ssh.NewConfigFromBytes -> ssh.ParseConfig
• Repurposes the previously unused ResolveHostName function, and then uses it
• Makes ssh.LoadConfig return an error, forcing callers to handle it

Checklist

• 🤖 This change is covered by tests as required.
• 🤹 All required manual testing has been performed.
• 📖 All documentation updates are complete.

[th3james]

This codifies the existing behaviour, but does call into question whether or not this is desirable

[awphi]

What's undesirable? The prepending of ssh://? If yes I've got no strong opinions but an argument in favour of leaving it is you want to write something like:

# compose.yaml
x-topo:
  deployment_success_message: "Check out your new deployed application on the target with `ssh ${TOPO_TARGET} 'cat /my/cool/thing'`"

This wouldn't work anymore if we removed the prepending since Topo happily accepts things like --target localhost:2222, an invalid ssh destination.