Add AWS purchasing options documentation

[Copilot]

Description

Adds documentation for AWS Lambda purchasing options to help users optimize costs for Architect applications at scale.

Changes

• New documentation page: aws-purchasing-options.md in Developer experience section

  • On-demand pricing (default): pay-per-use with no commitments
  • Compute Savings Plans: up to 66% savings for predictable workloads
  • Decision matrix for choosing pricing model based on usage patterns
  • Cost optimization tools (AWS Cost Explorer, recommendations workflow)
  • Clarifies Lambda does not support Reserved Instances (EC2-only)

• Navigation: Added to table of contents after "Create AWS credentials"

Screenshot

---

Thank you for helping out! ✨

We really appreciate your commitment to improving Architect

To maintain a high standard of quality in our releases, before merging every pull request we ask that you've completed the following:

• Forked the repo and created your branch from main
• Made sure tests pass (run npm it from the repo root)
• Updated relevant documentation internal to this repo (e.g. readme.md, help docs, inline docs & comments, etc.)
• Linked to any related issues, PRs, etc. below that may relate to, consume, or necessitate these changes

Please also be sure to completed the CLA as it's required for your PR to be merged. A github comment will prompt you if you haven't already.

Learn more about contributing to Architect here.

Thanks again!

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.