Enable and Configure Backups for a Server Action

## Affects:
Server Actions

## Need for this:
Links the enable and configure backups action API

## Hetzner API documentation
https://docs.hetzner.cloud/#server-actions-enable-and-configure-backups-for-a-server

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