Builds normalized SSH connection options for a machine map.

Supported auth types are:
- "password" with :auth-secret as the password
- "private-key" with :auth-secret as a readable private key path

Executes a shell command locally for localhost targets, otherwise over SSH.

Executes a shell command on a remote machine over SSH.

Returns true when the machine should be treated as the local host.

Bootstraps passwordless SSH for one already-compatible group of machines.

Groups machines by compatible SSH authentication details and bootstraps
passwordless SSH within each eligible group.