[management] Add Agent Network managed proxy to the API spec (#7433)

Defines the cloud-side managed gateway provisioning surface
(POST/GET /api/integrations/agent-network/managed-proxy) and its
response objects so clients consume generated types instead of
hand-written ones. POST is idempotent: 202 when the call starts (or
restarts) provisioning, 200 when a deployment already exists; 409
names an already-assigned endpoint the managed flow does not own and
503 signals temporarily exhausted endpoint allocation.

client/proto/generate.sh

@@ -1,4 +1,4 @@
-#!/bin/bash
+#!/usr/bin/env bash
 set -e
 
 if ! which realpath >/dev/null 2>&1; then