Machine ID: Switch to using new tsh-less SSH proxying by defualt and deprecate old tsh-ful proxying

[strideynet]

Thanks to the scale team, we have a new improved way of proxying SSH connections. We didn't adjust the generated ssh_config to start using this though, this issue covers that.

We should start using the new method by default in v16, and provide an escape-hatch to revert to the previous behaviour. In addition, we should publish a warning for users who have hand-written ssh_config and that they need to switch to the new invocation.

There may be some documentation we need to update that may say that tsh is required, this is no longer the case.

[strideynet]

Closed by #41482