docs: add enableOpenCode to awf-config.schema.json apiProxy section

Agent-Logs-Url: https://github.com/github/gh-aw-firewall/sessions/ef9327d6-049f-4c3a-b9e5-57a686f69790

Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>

Author: Copilot

docs/awf-config.schema.json

@@ -35,6 +35,7 @@
       "additionalProperties": false,
       "properties": {
         "enabled": { "type": "boolean" },
+        "enableOpenCode": { "type": "boolean" },
         "targets": {
           "type": "object",
           "additionalProperties": false,