[Fleet] Add unprivileged mapping to .fleet-agents (#108293)

Author: juliaElastic

x-pack/plugin/core/template-resources/src/main/resources/fleet-agents.json

@@ -99,6 +99,9 @@
                     "upgradeable": {
                       "type": "boolean"
                     },
+                    "unprivileged": {
+                      "type": "boolean"
+                    },
                     "version": {
                       "type": "text",
                       "fields": {