feat: Add Amazon Bedrock integration for LLM, embeddings, and reranking

[AlonsoDeCosio]

Summary

Brief description of the changes in this PR.

Type of Change

• Bug fix
• New feature
• Performance improvement
• Documentation/Tests

Objective

For new features and performance improvements:
This integration expands Graphiti's LLM provider support to include Amazon Bedrock, enabling users to:

• Use Bedrock models for LLM inference
• Leverage Bedrock embedding models for semantic search
• Utilize Cohere and Amazon rerank models for result reranking
• Take advantage of AWS's managed foundation model service with enterprise security and compliance

The integration follows Graphiti's established patterns and provides a complete solution with proper async support, error handling, and region-specific model validation.

Testing

• Unit tests added/updated
• Integration tests added/updated
• All existing tests pass

Breaking Changes

• This PR contains breaking changes

Checklist

• Code follows project style guidelines (make lint passes)
• Self-review completed
• Documentation updated where necessary
• No secrets or sensitive information committed

Related Issues

N/A - New feature addition

[danielchalef]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[AlonsoDeCosio]

I have read the CLA Document and I hereby sign the CLA

[AlonsoDeCosio]

recheck