net/nats-server: add reload command to rc.d script

Add a reload command to the rc.d script that uses NATS server's built-in
configuration reload functionality via the --signal reload option. This allows
users to reload the NATS configuration without a full service restart.

Also document the available extra commands (reload, logrotate, ldm) in the rc.d
script header for better discoverability.

PR: 252130
Reported by: nabbisen@yahoo.com