Add aws_bedrock_runtime_endpoint support

[Manouchehri]

This expands upon #717.

Future example usage (seems like Cloudflare AI Gateway has a bug atm :P ):

model_list:
  - model_name: claude-v2.1
    litellm_params:
      model: bedrock/anthropic.claude-v2:1
      aws_region_name: us-east-1
      aws_bedrock_runtime_endpoint: https://gateway.ai.cloudflare.com/v1/1234_account_id_here/demo/aws-bedrock/bedrock-runtime/us-east-1
  - model_name: claude-v2.1
    litellm_params:
      model: bedrock/anthropic.claude-v2:1
      aws_region_name: us-west-2
      aws_bedrock_runtime_endpoint: https://gateway.ai.cloudflare.com/v1/1234_account_id_here/demo/aws-bedrock/bedrock-runtime/us-west-2
  - model_name: claude-v2.1
    litellm_params:
      model: bedrock/anthropic.claude-v2:1
      aws_region_name: eu-central-1
      aws_bedrock_runtime_endpoint: https://gateway.ai.cloudflare.com/v1/1234_account_id_here/demo/aws-bedrock/bedrock-runtime/eu-central-1

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Name	Status	Preview	Comments	Updated (UTC)
litellm	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Dec 21, 2023 0:35am

[krrishdholakia]

LGTM!