cephadm: report intentionally stopped daemons as stopped

cephadm: report intentionally stopped daemons as stopped

node-exporter exits with status 143 when terminated via SIGTERM.
Systemd treats this as a failure by default, causing cephadm to
report an intentionally stopped daemon as being in an error state.

Allow daemon forms to provide daemon-specific success exit status
codes and generate a corresponding systemd SuccessExitStatus
drop-in when required.

For node-exporter, configure exit status 143 as successful so
intentional stops are reported as stopped rather than failed.

Fixes: https://tracker.ceph.com/issues/68863
Signed-off-by: Shubha Jain <SHUBHA.JAIN1@ibm.com>