Add ZoneIndex to PID zone

Adding ZoneIndex, an optional numeric parameter.

This was already implemented a while ago:
https://gerrit.openbmc.org/c/openbmc/phosphor-pid-control/+/36626

Signed-off-by: Josh Lehan <krellan@google.com>
Change-Id: Id4565599c19f9ebb483b488eeeb51d8e40aa82ad
diff --git a/schemas/pid_zone.json b/schemas/pid_zone.json
index 7713dae..740f426 100644
--- a/schemas/pid_zone.json
+++ b/schemas/pid_zone.json
@@ -24,6 +24,9 @@
                 },
                 "UpdateThermalsTimeMS": {
                     "type": "number"
+                },
+                "ZoneIndex": {
+                    "type": "number"
                 }
             },
             "required": ["FailSafePercent", "MinThermalOutput", "Name", "Type"]