Resolves issue-16844 - systemd notify by default

* updates `consul.service` systemd service unit to use `Type=notify` to
  resolve issue #16844
* add changelog update to match

.changelog/16845.txt

@@ -0,0 +1,3 @@
+```release-note:improvement
+systemd: set service type to notify.
+```

.release/linux/package/usr/lib/systemd/system/consul.service

@@ -6,6 +6,7 @@ After=network-online.target
 ConditionFileNotEmpty=/etc/consul.d/consul.hcl
 
 [Service]
+Type=notify
 EnvironmentFile=-/etc/consul.d/consul.env
 User=consul
 Group=consul