make auto-setting the encodings optional, alow explicitly setting it (#10774)

I was trying to use web loaders on some spanish documentation (e.g.
[this site](https://www.fromdoppler.com/es/mailing-tendencias/), but the
auto-encoding introduced in
https://github.com/langchain-ai/langchain/pull/3602 was detected as
"MacRoman" instead of the (correct) "UTF-8".

To address this, I've added the ability to disable the auto-encoding, as
well as the ability to explicitly tell the loader what encoding to use.

- **Description:** Makes auto-setting the encoding optional in
`WebBaseLoader`, and introduces an `encoding` option to explicitly set
it.
  - **Dependencies:** N/A
  - **Tag maintainer:** @hwchase17 
  - **Twitter handle:** @czue

libs/langchain/langchain/document_loaders/web_base.py

@@ -63,6 +63,8 @@ class WebBaseLoader(BaseLoader):
         verify_ssl: Optional[bool] = True,
         proxies: Optional[dict] = None,
         continue_on_failure: Optional[bool] = False,
+        autoset_encoding: Optional[bool] = True,
+        encoding: Optional[str] = None,
     ):
         """Initialize with webpage path."""
 
@@ -98,7 +100,8 @@ class WebBaseLoader(BaseLoader):
         self.session.headers = dict(headers)
         self.session.verify = verify_ssl
         self.continue_on_failure = continue_on_failure
-
+        self.autoset_encoding = autoset_encoding
+        self.encoding = encoding
         if proxies:
             self.session.proxies.update(proxies)
 
@@ -208,6 +211,10 @@ class WebBaseLoader(BaseLoader):
         html_doc = self.session.get(url, **self.requests_kwargs)
         if self.raise_for_status:
             html_doc.raise_for_status()
+
+        if self.encoding is not None:
+            html_doc.encoding = self.encoding
+        elif self.autoset_encoding:
             html_doc.encoding = html_doc.apparent_encoding
         return BeautifulSoup(html_doc.text, parser)