feat: Adding portkey.ai gateway as a custom model

[fede-dash]

📄 Description

This PR adds a new documentation page at docs/portkey.md that introduces Portkey as a supported provider in the Strands SDK. It includes:

• A clear explanation of what Portkey is and how it integrates into the SDK.
• Installation instructions for enabling Portkey as an optional dependency.
• A complete Python usage example using PortkeyModel with Agent.
• A configuration table documenting all supported parameters.
• Troubleshooting guidance for common setup issues.
• References to official Portkey and OpenAI resources.

This documentation enables developers to adopt Portkey with confidence and flexibility across OpenAI, Anthropic (via Bedrock), and other models.

🔀 Type of Change

• New content addition
• Content update/revision
• Structure/organization improvement
• Typo/formatting fix
• Bug fix
• Other (please describe):

💡 Motivation and Context

Portkey support was recently added to the Strands SDK to provide unified access to multiple LLM providers through a single abstraction. This documentation ensures developers can:

• Understand the purpose and benefits of Portkey.
• Correctly install and configure Portkey in the SDK.
• Use the correct parameters, authentication setup, and provider selection.
• Reference real-world scenarios and best practices.

It also sets the foundation for future features like multi-modal input support and dynamic routing configurations.

🗂️ Areas Affected

• docs/portkey.md — New documentation page added, covering:
  • Overview of Portkey
  • Installation instructions
  • Usage example with code
  • Configuration options table
  • Troubleshooting notes
  • Reference links to relevant external docs

📸 Screenshots

Not applicable — this is a text-only documentation change. Code examples are included in the markdown file.

✅ 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 documentation tests pass

📝 Additional Notes

This update ensures the SDK is plug-and-play for organizations already using Portkey (e.g., Notion, Ramp, Descript). It supports common production needs such as observability, routing, authentication, and retry logic.

🔗 For broader implementation details, see: Portkey Integration for Strands SDK

---

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