models - DeepSeek documentation support

[veeragoni]

Add comprehensive DeepSeek model provider support

Description

Added complete documentation and examples for DeepSeek model provider integration with Strands Agents SDK, including support for both chat and reasoning models with Fill-in-the-Middle (FIM) capabilities.

Type of Change

• New content addition

Motivation and Context

DeepSeek models have been implemented in the SDK and need comprehensive documentation to help users leverage their unique capabilities, particularly the reasoning model for complex problem-solving and FIM for code completion tasks.

Areas Affected

• docs/user-guide/concepts/model-providers/deepseek.md - New model provider documentation
• docs/user-guide/quickstart.md - Added DeepSeek to model provider list
• docs/examples/python/deepseek_reasoning_agent.py - New comprehensive example
• docs/examples/python/deepseek_reasoning_agent.md - Example documentation
• docs/examples/python/deepseek_code_completion.py - New FIM-focused example
• docs/examples/python/deepseek_code_completion.md - Code completion documentation
• mkdocs.yml - Updated navigation structure

Screenshots

N/A - Text-based documentation changes

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

The documentation covers:

• Basic DeepSeek chat model usage
• Advanced reasoning model capabilities
• Fill-in-the-Middle (FIM) code completion
• Structured output with reasoning
• Configuration options and best practices
• Comprehensive examples for various use cases

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