Add After and Wants dependancies on chronyd.service to systemd unit file

Please add "After" and "Wants" dependencies on the chronyd.service to the amazon-ssm-agent.service unit file to prevent errors like
```
2023-11-07 00:48:23 ERROR [CredentialRefresher] Retrieve credentials produced error: unexpected error getting instance profile role credentials or calling UpdateInstanceInformation. Skipping default host management fallback: retrieved credentials failed to report to ssm. RequestId: 87b14e5a-ef87-450e-a20d-fa375bef5127 Error: InvalidSignatureException: Signature expired: 20231106T134822Z is now earlier than 20231106T144933Z (20231106T145433Z - 5 min.)
```
which can happen to instances/VMs which are restarting after a period of powerloss.

Open the amazon-ssm-agent.service unit file and inspect its dependency declarations. Confirm where the chronyd.service ordering and startup dependencies belong, then verify that the unit expresses the requested After and Wants relationships so chronyd is available after restart from power loss.

Written by the indexing model from the issue text.