Disable passwordless ssh into server.

When re-running
```bash
./src/main.sh \
--1-domain-1-service \
--setup-ssh-client \
--set-server-username \
--set-server-ssh-onion .onion \
--get-server-gif
```
The pre-requisites generate a new private-public key pair and add it to the server. To allow that, the server asks the client the server password. This may only be done once, and then the server should not allow password login anymore.

- [ ] Actively disable password login on server after client has received ssh access with private-public key pair.