docs: add PromptCachingHook example to Bedrock documentation

[moritalous]

Add simplified message caching example using PromptCachingHook with note on minimum token requirements for cache creation.

Description

Added a new "Automatic Message Caching with PromptCachingHook (Simplified)" section to the Amazon Bedrock documentation. This provides users with a practical example of using PromptCachingHook for automatic cache point management, simplifying the message caching
workflow compared to manual cache point management.

The section includes:

• Python code example with imports and usage patterns
• Explanation of automatic cache point lifecycle (add before invocation, remove after)
• Important note about minimum token requirements (1,024+) for cache creation
• TypeScript support status indication

Related Issues

strands-agents/sdk-python#1508

Type of Change

• Content update/revision

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

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