community[minor]: allow enabling proxy in aiohttp session in AsyncHTML (#19499)

Allow enabling proxy in aiohttp session async html

docs/docs/integrations/document_loaders/async_html.ipynb

@@ -37,6 +37,10 @@
    "source": [
     "urls = [\"https://www.espn.com\", \"https://lilianweng.github.io/posts/2023-06-23-agent/\"]\n",
     "loader = AsyncHtmlLoader(urls)\n",
+    "# If you need to use the proxy to make web requests, for example using http_proxy/https_proxy environmental variables,\n",
+    "# please set trust_env=True explicitly here as follows:\n",
+    "# loader = AsyncHtmlLoader(urls, trust_env=True)\n",
+    "# Otherwise, loader.load() may stuck becuase aiohttp session does not recognize the proxy by default\n",
     "docs = loader.load()"
    ]
   },