[elicitations] Switch to use MCP style elicitation payload for mcp tool approvals. (#13621)

- [x] Switch to use MCP style elicitation payload for mcp tool
approvals.
- [ ] TODO: Update the UI to support the full spec.

codex-rs/app-server-protocol/schema/json/codex_app_server_protocol.v2.schemas.json

@@ -3349,6 +3349,7 @@
       "oneOf": [
         {
           "properties": {
+            "_meta": true,
             "message": {
               "type": "string"
             },
@@ -3369,6 +3370,7 @@
         },
         {
           "properties": {
+            "_meta": true,
             "elicitation_id": {
               "type": "string"
             },
@@ -4852,6 +4854,13 @@
             "server_name": {
               "type": "string"
             },
+            "turn_id": {
+              "description": "Turn ID that this elicitation belongs to, when known.",
+              "type": [
+                "string",
+                "null"
+              ]
+            },
             "type": {
               "enum": [
                 "elicitation_request"