feat: init enhancement for milo workflows

[zachsmith1]

This pull request adds a comprehensive design proposal for "Datum Workflows," an event-driven automation layer for Milo. The document outlines the motivation, goals, design details, testing and simulation requirements, production readiness considerations, and implementation phases for the feature. It sets the foundation for future development and research, focusing on safety, testability, and a strong operator experience.

Feature Proposal and Design:

• Introduces a declarative, event-driven workflow system for Milo, enabling teams to automate internal processes based on domain events, with a strong emphasis on safety, simulation, and impact analysis.
• Details requirements for a first-class Testing & Simulation UX, including dry-run capabilities, blast-radius estimates, and backtesting, ensuring users can preview workflow effects before enabling.
• Specifies goals such as multi-tenant isolation, action libraries, and integration with Kubernetes workflow engines (Argo/Tekton), while explicitly excluding building a workflow engine from scratch.