Add comprehensive secrets management tools guide for 2025

Create evergreen article covering 25+ secrets management tools across 6 categories with strategic Pulumi ESC positioning as premier secrets orchestration platform. Features paragraph-centric content, internal Pulumi.com links, and balanced educational coverage while naturally guiding readers toward ESC as optimal choice for modern configuration-as-code workflows.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: asafashirov