docs(bedrock): add guardrail_last_turn_only docs

[aiancheruk]

Description

Added documentation for the new guardrail_last_turn_only parameter in BedrockModel. This feature allows users to optimize guardrail evaluation by sending only the most recent conversation turn instead of the full conversation history.

Type of Change

• New content addition
• Content update/revision

Motivation and Context

The guardrail_last_turn_only parameter was added to the BedrockModel class. This documentation update ensures users are aware of this new feature and understand:

• How to use the parameter
• When to enable it (performance optimization, cost reduction, conversation recovery)
• The benefits it provides over full conversation history evaluation

Areas Affected

• docs/user-guide/concepts/model-providers/amazon-bedrock.md

  • Configuration Options table (added new parameter row)
  • Guardrails section (updated code example and added explanation)

• docs/user-guide/safety-security/guardrails.md

  • Amazon Bedrock section (updated code example and added performance optimization note)

Screenshots

Checklist

• I have read the CONTRIBUTING document
• My changes follow the project's documentation style
• I have tested the documentation locally using mkdocs serve
• Links in the documentation are valid and working
• Images/diagrams are properly sized and formatted
• All new and existing tests pass

Additional Notes

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.