Handle SSH config conflicts better

[code-asher]

I think we will need to prepend the config to avoid being clobbered by Host * configs further up in the stack.

But we should also change the host name because it is probably not uncommon to have a *.mycompany.com entry. We could prepend the URL or swap it with the agent name. Or obfuscate the domain in some way.

[code-asher]

In the VS Code plugin we do coder-vscode.host--, so maybe we can do coder-jetbrains.dev.coder.com--.

Need to make sure existing connections still work after the change. Maybe as part of configuring SSH, we go through the recent connections and update the host names to the new format.