MB-43675 Part 0: GSI Audit Service integration feature

Deliver just the GSI audit_descriptor.json file. This is unused until a
reference to it is delivered to kv_engine/auditd/etc/module_descriptors.json,
but it must be present before the KV entry or KV build will fail.

KV JSON file is teed up here:
http://review.couchbase.org/c/kv_engine/+/156141

Change-Id: I1402d8dd14463a2cd695af2ac5f0fd074617c888

secondary/audit/audit_descriptor.json

@@ -0,0 +1,46 @@
+{
+  "version": 2,
+  "module": "index",
+  "events": [
+    {
+      "id": 49152,
+      "name": "HTTP 401: Unauthorized",
+      "description": "Authentication is required to access the requested resource",
+      "sync": false,
+      "enabled": true,
+      "mandatory_fields": {
+        "timestamp": "",
+        "real_userid": {"domain": "", "user": ""},
+        "remote": {"ip": "", "port": 1},
+        "local": {"ip": "", "port": 1},
+
+        "service": "",
+        "method": "",
+        "url": ""
+      },
+      "optional_fields": {
+        "message": ""
+      }
+    },
+    {
+      "id": 49153,
+      "name": "HTTP 403: Forbidden",
+      "description": "The user does not have permission to access the requested resource",
+      "sync": false,
+      "enabled": true,
+      "mandatory_fields": {
+        "timestamp": "",
+        "real_userid": {"domain": "", "user": ""},
+        "remote": {"ip": "", "port": 1},
+        "local": {"ip": "", "port": 1},
+
+        "service": "",
+        "method": "",
+        "url": ""
+      },
+      "optional_fields": {
+        "message": ""
+      }
+    }
+  ]
+}