Feat bedrock cohere support (#11230)

**Description:**
Added support for Cohere command model via Bedrock.
With this change it is now possible to use the `cohere.command-text-v14`
model via Bedrock API.

About Streaming: Cohere model outputs 2 additional chunks at the end of
the text being generated via streaming: a chunk containing the text
`<EOS_TOKEN>`, and a chunk indicating the end of the stream. In this
implementation I chose to ignore both chunks. An alternative solution
could be to replace `<EOS_TOKEN>` with `\n`

Tests: manually tested that the new model work with both
`llm.generate()` and `llm.stream()`.
Tested with `temperature`, `p` and `stop` parameters.

**Issue:** #11181 

**Dependencies:** No new dependencies

**Tag maintainer:** @baskaryan 

**Twitter handle:** mangelino

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

libs/langchain/langchain/llms/bedrock.py

@@ -65,6 +65,7 @@ class LLMInputOutputAdapter:
     provider_to_output_key_map = {
         "anthropic": "completion",
         "amazon": "outputText",
+        "cohere": "text",
     }
 
     @classmethod
@@ -74,7 +75,7 @@ class LLMInputOutputAdapter:
         input_body = {**model_kwargs}
         if provider == "anthropic":
             input_body["prompt"] = _human_assistant_format(prompt)
-        elif provider == "ai21":
+        elif provider == "ai21" or provider == "cohere":
             input_body["prompt"] = prompt
         elif provider == "amazon":
             input_body = dict()
@@ -98,6 +99,8 @@ class LLMInputOutputAdapter:
 
         if provider == "ai21":
             return response_body.get("completions")[0].get("data").get("text")
+        elif provider == "cohere":
+            return response_body.get("generations")[0].get("text")
         else:
             return response_body.get("results")[0].get("outputText")
 
@@ -119,6 +122,12 @@ class LLMInputOutputAdapter:
             chunk = event.get("chunk")
             if chunk:
                 chunk_obj = json.loads(chunk.get("bytes").decode())
+                if provider == "cohere" and (
+                    chunk_obj["is_finished"]
+                    or chunk_obj[cls.provider_to_output_key_map[provider]]
+                    == "<EOS_TOKEN>"
+                ):
+                    return
 
                 # chunk obj format varies with provider
                 yield GenerationChunk(
@@ -159,6 +168,7 @@ class BedrockBase(BaseModel, ABC):
         "anthropic": "stop_sequences",
         "amazon": "stopSequences",
         "ai21": "stop_sequences",
+        "cohere": "stop_sequences",
     }
 
     @root_validator()
@@ -259,9 +269,10 @@ class BedrockBase(BaseModel, ABC):
 
             # stop sequence from _generate() overrides
             # stop sequences in the class attribute
-            _model_kwargs[
-                self.provider_stop_sequence_key_name_map.get(provider),
-            ] = stop
+            _model_kwargs[self.provider_stop_sequence_key_name_map.get(provider)] = stop
+
+        if provider == "cohere":
+            _model_kwargs["stream"] = True
 
         params = {**_model_kwargs, **kwargs}
         input_body = LLMInputOutputAdapter.prepare_input(provider, prompt, params)