langchain[minor], community[minor]: add CrossEncoderReranker with HuggingFaceCrossEncoder and SagemakerEndpointCrossEncoder (#13687)

- **Description:** Support reranking based on cross encoder models
available from HuggingFace.
      - Added `CrossEncoder` schema
- Implemented `HuggingFaceCrossEncoder` and
`SagemakerEndpointCrossEncoder`
- Implemented `CrossEncoderReranker` that performs similar functionality
to `CohereRerank`
- Added `cross-encoder-reranker.ipynb` to demonstrate how to use it.
Please let me know if anything else needs to be done to make it visible
on the table-of-contents navigation bar on the left, or on the card list
on [retrievers documentation
page](https://python.langchain.com/docs/integrations/retrievers).
  - **Issue:** N/A
  - **Dependencies:** None other than the existing ones.

---------

Co-authored-by: Kenny Choe <kchoe@amazon.com>
Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/community/langchain_community/cross_encoders/base.py

@@ -0,0 +1,17 @@
+from abc import ABC, abstractmethod
+from typing import List, Tuple
+
+
+class BaseCrossEncoder(ABC):
+    """Interface for cross encoder models."""
+
+    @abstractmethod
+    def score(self, text_pairs: List[Tuple[str, str]]) -> List[float]:
+        """Score pairs' similarity.
+
+        Args:
+            text_pairs: List of pairs of texts.
+
+        Returns:
+            List of scores.
+        """