fix: allow image based deployment without user-data

[m-bucher]

Not perfect but should be sufficient to use image based deployment without user-data images.

[sbernhard]

we should fix the FIXME and TODOs first

[m-bucher]

Adding Key during host-creations apparently does not work, because it breaks with on the 2nd created host:

09:32:28 rails.1   |  07bf2b05 | Error: API request failed
09:32:28 rails.1   |  07bf2b05 | 
09:32:28 rails.1   |  07bf2b05 |   with hcloud_ssh_key.deploy_key,
09:32:28 rails.1   |  07bf2b05 |   on main.tf line 24, in resource "hcloud_ssh_key" "deploy_key":
09:32:28 rails.1   |  07bf2b05 |   24: resource "hcloud_ssh_key" "deploy_key" {
09:32:28 rails.1   |  07bf2b05 | 
09:32:28 rails.1   |  07bf2b05 | An unexpected error was encountered during an API request.
09:32:28 rails.1   |  07bf2b05 | 
09:32:28 rails.1   |  07bf2b05 | SSH key not unique (uniqueness_error, 26c9f22aa91213688512d1c4f2f64f28)
09:32:28 rails.1   |  07bf2b05 | 
09:32:28 rails.1   |  07bf2b05 | Error code: uniqueness_error
09:32:28 rails.1   |  07bf2b05 | Status code: 409
09:32:28 rails.1   |  07bf2b05 | 
09:32:28 rails.1   |  07bf2b05 | )