Add Attach an ISO to server action

## Affects:
Server Actions

## Need for this:
Links the attach an iso to server API

## Hetzner API documentation
https://docs.hetzner.cloud/#server-actions-attach-an-iso-to-a-server

## Tasks
- [ ] Implement method on Server class
- [ ] Add new Action enum
- [ ] Implement change in ServerChangeListener
- [ ] Implement change in ServerService
- [ ] Add testing