Bedrock llm and embeddings (#5464)

# Bedrock LLM and Embeddings
This PR adds a new LLM and an Embeddings class for the
[Bedrock](https://aws.amazon.com/bedrock) service. The PR also includes
example notebooks for using the LLM class in a conversation chain and
embeddings usage in creating an embedding for a query and document.

**Note**: AWS is doing a private release of the Bedrock service on
05/31/2023; users need to request access and added to an allowlist in
order to start using the Bedrock models and embeddings. Please use the
[Bedrock Home Page](https://aws.amazon.com/bedrock) to request access
and to learn more about the models available in Bedrock.

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docs/integrations/bedrock.md

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+# Amazon Bedrock
+
+>[Amazon Bedrock](https://aws.amazon.com/bedrock/) is a fully managed service that makes FMs from leading AI startups and Amazon available via an API, so you can choose from a wide range of FMs to find the model that is best suited for your use case.
+
+## Installation and Setup
+
+```bash
+pip install boto3
+```
+
+## LLM
+
+See a [usage example](../modules/models/llms/integrations/bedrock.ipynb).
+
+```python
+from langchain import Bedrock
+```
+
+## Text Embedding Models
+
+See a [usage example](../modules/models/text_embedding/examples/bedrock.ipynb).
+```python
+from langchain.embeddings import BedrockEmbeddings
+```