community[minor]: add proxy support to RecursiveUrlLoader (#27364)

**Description**
This PR introduces the proxies parameter to the RecursiveUrlLoader
class, allowing the user to specify proxy servers for requests. This
update enables crawling through proxy servers, providing enhanced
flexibility for network configurations.
The key changes include:
  1.Added an optional proxies parameter to the constructor (__init__).
2.Updated the documentation to explain the proxies parameter usage with
an example.
3.Modified the _get_child_links_recursive method to pass the proxies
parameter to the requests.get function.



**Sample Usage**

```python
from bs4 import BeautifulSoup as Soup
from langchain_community.document_loaders.recursive_url_loader import RecursiveUrlLoader

proxies = {
    "http": "http://localhost:1080",
    "https": "http://localhost:1080",
}
url = "https://python.langchain.com/docs/concepts/#langchain-expression-language-lcel"
loader = RecursiveUrlLoader(
    url=url, max_depth=1, extractor=lambda x: Soup(x, "html.parser").text,proxies=proxies
)
docs = loader.load()
```

---------

Co-authored-by: root <root@thb>

docs/docs/security.md

@@ -6,7 +6,7 @@ LangChain has a large ecosystem of integrations with various external resources
 
 When building such applications developers should remember to follow good security practices:
 
-* [**Limit Permissions**](https://en.wikipedia.org/wiki/Principle_of_least_privilege): Scope permissions specifically to the application's need. Granting broad or excessive permissions can introduce significant security vulnerabilities. To avoid such vulnerabilities, consider using read-only credentials, disallowing access to sensitive resources, using sandboxing techniques (such as running inside a container), etc. as appropriate for your application.
+* [**Limit Permissions**](https://en.wikipedia.org/wiki/Principle_of_least_privilege): Scope permissions specifically to the application's need. Granting broad or excessive permissions can introduce significant security vulnerabilities. To avoid such vulnerabilities, consider using read-only credentials, disallowing access to sensitive resources, using sandboxing techniques (such as running inside a container), specifying proxy configurations to control external requests, etc. as appropriate for your application.
 * **Anticipate Potential Misuse**: Just as humans can err, so can Large Language Models (LLMs). Always assume that any system access or credentials may be used in any way allowed by the permissions they are assigned. For example, if a pair of database credentials allows deleting data, it’s safest to assume that any LLM able to use those credentials may in fact delete data.
 * [**Defense in Depth**](https://en.wikipedia.org/wiki/Defense_in_depth_(computing)): No security technique is perfect. Fine-tuning and good chain design can reduce, but not eliminate, the odds that a Large Language Model (LLM) may make a mistake. It’s best to combine multiple layered security approaches rather than relying on any single layer of defense to ensure security. For example: use both read-only permissions and sandboxing to ensure that LLMs are only able to access data that is explicitly meant for them to use.
 

libs/community/langchain_community/document_loaders/recursive_url_loader.py

@@ -268,6 +268,7 @@ def __init__(
         base_url: Optional[str] = None,
         autoset_encoding: bool = True,
         encoding: Optional[str] = None,
+        proxies: Optional[dict] = None,
     ) -> None:
         """Initialize with URL to crawl and any subdirectories to exclude.
 
@@ -313,6 +314,16 @@ def simple_metadata_extractor(
                 encoding, unless the `encoding` argument has already been explicitly set.
             encoding: The encoding of the response. If manually set, the encoding will be
                 set to given value, regardless of the `autoset_encoding` argument.
+            proxies: A dictionary mapping protocol names to the proxy URLs to be used for requests.
+                This allows the crawler to route its requests through specified proxy servers.
+                If None, no proxies will be used and requests will go directly to the target URL.
+                Example usage:
+                ..code-block:: python
+
+                    proxies = {
+                        "http": "http://10.10.1.10:3128",
+                        "https": "https://10.10.1.10:1080",
+                    }
         """  # noqa: E501
 
         self.url = url
@@ -342,6 +353,7 @@ def simple_metadata_extractor(
         self.check_response_status = check_response_status
         self.continue_on_failure = continue_on_failure
         self.base_url = base_url if base_url is not None else url
+        self.proxies = proxies
 
     def _get_child_links_recursive(
         self, url: str, visited: Set[str], *, depth: int = 0
@@ -360,7 +372,9 @@ def _get_child_links_recursive(
         # Get all links that can be accessed from the current URL
         visited.add(url)
         try:
-            response = requests.get(url, timeout=self.timeout, headers=self.headers)
+            response = requests.get(
+                url, timeout=self.timeout, headers=self.headers, proxies=self.proxies
+            )
 
             if self.encoding is not None:
                 response.encoding = self.encoding