Update ceph-salt pillar example

When `ceph-salt-formula` is installed, a `pillar.example` file is created, but this example is outdated/incomplete so it needs to be updated:
```
master:~ # cat /usr/share/salt-formulas/metadata/ceph-salt/pillar.example
ceph-salt:
minions:
-
-
# ...
bootstrap_minion:
ssh:
private_key: |


# ...

public_key:
time_server:
enabled: True
host_server:
external_time_servers:
-
-
# ...
```

Inspect /usr/share/salt-formulas/metadata/ceph-salt/pillar.example and compare it with the current ceph-salt pillar configuration requirements. Update the example so it is complete and current, then verify that the shown minion, SSH, and time-server settings accurately represent supported configuration.

Written by the indexing model from the issue text.