fix (Html2TextTransformer): allow configuration of html2text (#9914)

Hi, this PR enables configuring the html2text package, instead of being
bound to use the hardcoded values. While simply passing `ignore_links`
and `ignore_images` to the `transform_documents` method was possible, I
preferred passing them to the `__init__` method for 2 reasons:

1. It is more efficient in case of subsequent calls to
`transform_documents`.
2. It allows to move the "complexity" to the instantiation, keeping the
actual execution simple and general enough. IMO the transformers should
all follow this pattern, allowing something like this:
```python
# Instantiate transformers
transformers = [
    TransformerA(foo='bar'),
    TransformerB(bar='foo'),
    # others
]

# During execution, call them sequentially
documents = ...
for tr in transformers:
    documents = tr.transform_documents(documents)
```

Thanks for the reviews!

---------

Co-authored-by: taamedag <Davide.Menini@swisscom.com>

libs/langchain/langchain/document_transformers/html2text.py

@@ -5,13 +5,22 @@ from langchain.schema import BaseDocumentTransformer, Document
 
 class Html2TextTransformer(BaseDocumentTransformer):
     """Replace occurrences of a particular search pattern with a replacement string
+
+    Arguments:
+        ignore_links: Whether links should be ignored; defaults to True.
+        ignore_images: Whether images should be ignored; defaults to True.
+
     Example:
         .. code-block:: python
             from langchain.document_transformers import Html2TextTransformer
-            html2text=Html2TextTransformer()
-            docs_transform=html2text.transform_documents(docs)
+            html2text = Html2TextTransformer()
+            docs_transform = html2text.transform_documents(docs)
     """
 
+    def __init__(self, ignore_links: bool = True, ignore_images: bool = True) -> None:
+        self.ignore_links = ignore_links
+        self.ignore_images = ignore_images
+
     def transform_documents(
         self,
         documents: Sequence[Document],
@@ -25,10 +34,11 @@ class Html2TextTransformer(BaseDocumentTransformer):
                 install it with `pip install html2text`"""
             )
 
-        # Create an html2text.HTML2Text object and override some properties
+        # Create a html2text.HTML2Text object and override some properties
         h = html2text.HTML2Text()
-        h.ignore_links = True
-        h.ignore_images = True
+        h.ignore_links = self.ignore_links
+        h.ignore_images = self.ignore_images
+
         for d in documents:
             d.page_content = h.handle(d.page_content)
         return documents