.ssh directory not created when provisioning machine

This can result in a `.ssh` _file_ being created that contains the `authorized_keys`, which is incorrect.

We should ensure that the `.ssh` directory exists prior to attempting to copy the file into place.

Thanks @spencertransier for figuring this out

https://github.com/Automattic/packer-plugin-hostmgr/blob/fb709070ac4d6da90df41756a5b3e45f7040682d/provisioner/provisioner.go#L101

Start in provisioner/provisioner.go around line 101, where the authorized_keys file is copied during machine provisioning. Trace the destination path and verify the .ssh directory is created before the copy is attempted. Done means authorized_keys is placed inside a .ssh directory rather than a file named .ssh; no test file is mentioned.

Written by the indexing model from the issue text.