add uptime and promote system to v1 (openconfig#985)

* add uptime and promote system to v1

release/models/system/openconfig-system.yang

@@ -47,7 +47,13 @@ module openconfig-system {
     Section 4.c of the IETF Trust's Legal Provisions Relating
     to IETF Documents (http://trustee.ietf.org/license-info).";
 
-  oc-ext:openconfig-version "0.17.1";
+  oc-ext:openconfig-version "1.0.0";
+
+revision "2023-10-26" {
+    description
+      "Add up-time leaf and promote module to version 1.0.";
+    reference "1.0.0";
+  }
 
   revision "2023-06-16" {
     description
@@ -371,6 +377,14 @@ module openconfig-system {
           "The current system date and time.";
     }
 
+    leaf up-time {
+        type oc-types:timeticks64;
+        units "nanoseconds";
+        description
+          "The amount of time since the network operating system was
+          initialized.";
+    }
+
     leaf boot-time {
         type oc-types:timeticks64;
         units "nanoseconds";