Improve: Dramatically enhance three more plugin type documentation pages

Expanded Notification, Option Values, and Storage plugin documentation with
comprehensive overviews, use cases, examples, and best practices to help
developers understand when and how to create these plugins.

Changes Summary:
- 1,871 lines added across 3 files
- Added comprehensive overviews, use cases, and comparisons
- Complete working examples for all plugin types
- Best practices and troubleshooting sections

notification-plugins.md (375 → 833 lines):
- Enhanced overview explaining what notifications do and when to create plugins
- Added comparison table of all 5 notification triggers with available data
- Improved "Plugin Implementation Types" section (Java vs Groovy comparison)
- Added complete Slack notification example with error handling (150+ lines)
- Enhanced Groovy section with complete webhook example
- Reorganized execution data reference (more scannable, less redundant)
- Consolidated async notifications configuration with use case guidance
- Added comprehensive best practices (error handling, logging, timeouts, security)
- Related documentation links

option-values-plugins.md (158 → 904 lines):
- Dramatically expanded overview with clear explanation of dynamic value generation
- Added "What They Do" and "When to Create" sections with specific use cases
- Common use cases organized by category (Infrastructure, Environment, Version, Integration)
- Comparison section showing when NOT to use vs when TO use
- Removed prominent feature flag section (moved to troubleshooting)
- Enhanced Java section with basic example and complete AWS regions API example
- Improved Groovy section with Kubernetes namespaces API example
- Dramatically enhanced Script section with complete examples:
  - Basic example with plugin.yaml
  - API integration example
  - External tools example (kubectl, rd CLI)
  - Environment variables table
- Added comprehensive best practices (performance, error handling, security, UX)
- Troubleshooting section
- Related documentation links

storage-plugins.md (38 → 446 lines):
- Complete rewrite with comprehensive overview
- Explained what Storage plugins are (WHERE/HOW secrets are stored)
- Added "What Storage Plugins Do" section with 6 key responsibilities
- Storage architecture explanation with visual tree structure
- "When to Create" section with enterprise integration scenarios
- Documented built-in providers (db, file) with pros/cons
- CRITICAL: Added "Storage Plugin vs Storage Converter Plugin" section
  - Explains WHERE (Storage) vs HOW (Converter)
  - Shows how they work together
  - Prevents major confusion between these two plugin types
- Path-based configuration explanation
- Complete Java implementation example (200+ lines) showing:
  - All Tree interface methods
  - File-based storage implementation
  - CRUD operations, directory listing, metadata handling
- Best practices (error handling, cleanup, thread safety, metadata)
- Added prominent references to Vault Storage plugin as open source example
- Related documentation links

Common Improvements Across All Three:
- Clear "What [Plugin] Does" sections
- "When to Create" guidance with specific scenarios
- Comparison sections distinguishing from other plugin types
- Complete working examples (not just snippets)
- Best practices sections
- Troubleshooting sections
- Related documentation links
- Customer-focused language

Benefits:
- Developers understand WHAT each plugin type does
- Clear guidance on WHEN to create vs use alternatives
- Working examples they can copy and adapt
- Best practices prevent common mistakes
- Much better developer experience

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: fdevans