Document Docker extensibility ideas

[Ulthran]

Summary

• add a brainstorming document outlining options to make the Docker images easier to extend

Testing

• not run

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https://chatgpt.com/codex/tasks/task_e_68eea342ce688323bdcf6711a3d238c8

[Copilot]

Pull Request Overview

This PR adds a brainstorming document that outlines strategies for making Sunbeam's Docker images more extensible. The document proposes five complementary approaches to address the current limitation where bundled conda environments make the images convenient but difficult to extend with new extensions or Python packages.

Key changes:

• Introduces a new markdown document with five distinct extensibility strategies
• Provides technical implementation details for each approach
• Suggests combining options for a minimal yet effective solution

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