leak detector: json schema definition

Define the json schema for leak detector and use it in expose elements
in global.json schema. The leak detector schema defines various
properties such as type, subtype, gpio pin name, gpio polarity, etc as
per design https://gerrit.openbmc.org/c/openbmc/docs/+/73152.

Related PR:
https://gerrit.openbmc.org/c/openbmc/phosphor-dbus-interfaces/+/75999

Change-Id: I82f674a982d57774f3616cf0064256f8feadf158
Signed-off-by: Jagpal Singh Gill <paligill@gmail.com>
diff --git a/schemas/global.json b/schemas/global.json
index 070f794..e9bc310 100644
--- a/schemas/global.json
+++ b/schemas/global.json
@@ -38,6 +38,9 @@
                     "$ref": "virtual_sensor.json#/$defs/VirtualSensor"
                 },
                 {
+                    "$ref": "leak_detector.json#/$defs/GPIOLeakDetector"
+                },
+                {
                     "description": "Ensure the parent anyOf schema does not validate when an element does not define a type property.",
                     "not": {
                         "required": ["Type"]