Support for custom models imported in [Bedrock](https://docs.aws.amazon.com/bedrock/latest/userguide/model-customization-import-model.html).

[krrishdholakia]

          Support for custom models imported in [Bedrock](https://docs.aws.amazon.com/bedrock/latest/userguide/model-customization-import-model.html).

Use case: we have a fine-tuned model deployed in Bedrock. The tuned model is based on OpenOrca, so the start and end tokens are different than instruct version.

If the provider is mistral, the template uses the instruct template rather than OpenOrca's.

  response = client.invoke_model(
      body={"prompt": "<s>[INST] hello, tell me a joke [/INST]\n", "max_tokens": 1024, "temperature": 0},
      modelId=<model_id>,
      accept=accept,
      contentType=contentType
  )

Tokens<|im_start|> and <|im_end|> should be used instead.

Tried using a custom provider as a workaround. However, the body is empty and the request fails:

  response = client.invoke_model(
      body={},
      modelId=<model_id>,
      accept=accept,
      contentType=contentType
  )

The only thing we need is that prompt template configuration is respected, as it is done with amazon or anthropic providers.

      model_id: "model_arn"
      roles: {"system":{"pre_message":"<|im_start|>system\n", "post_message":"<|im_end|>"}, "assistant":{"pre_message":"<|im_start|>assistant\n","post_message":"<|im_end|>"}, "user":{"pre_message":"<|im_start|>user\n","post_message":"<|im_end|>"}}
      bos_token: "<s>"
      eos_token: "<|im_end|>"

litellm/litellm/llms/bedrock.py

Lines 743 to 746 in 3a35a58

	elif provider == "mistral":
	prompt = prompt_factory(
	model=model, messages=messages, custom_llm_provider="bedrock"
	)

Originally posted by @andresd95 in #361 (comment)