Add Best Practices documentation section (Phase 2.1)

This commit completes Phase 2.1 of the documentation expansion plan by adding
comprehensive best practices documentation for psake build scripts.

New Documentation Added:
- Best Practices category (_category_.json)
- Organizing Large Scripts (organizing-large-scripts.md)
  - File structure patterns (by category and build type)
  - Modular task files with complete examples
  - Using Include effectively with path validation
  - Shared utilities (file operations, logging, versioning)
  - Complete large project example

- Environment Management (environment-management.md)
  - Environment configuration patterns (inline, external files, JSON/YAML)
  - Environment-specific properties for dev/staging/prod
  - Conditional task execution using preconditions
  - Complete environment management example
  - CI/CD integration (GitHub Actions, Azure Pipelines)

- Secret Management (secret-management.md)
  - Environment variable patterns
  - Secure strings (PowerShell DPAPI)
  - Azure Key Vault integration
  - AWS Secrets Manager integration
  - HashiCorp Vault integration
  - Security best practices (never commit secrets, avoid logging)
  - Secure certificate handling

- Testing Build Scripts (testing-build-scripts.md)
  - Pester test setup and structure
  - Testing task dependencies
  - Mocking external commands (dotnet, az, AWS CLI)
  - Integration tests
  - Error handling tests
  - Test-friendly build script patterns
  - CI/CD integration

- Build Versioning Strategies (versioning-strategy.md)
  - Semantic versioning (SemVer) with pre-release labels
  - Git-based versioning from tags
  - GitVersion tool integration
  - CI build number versioning (GitHub Actions, Azure Pipelines)
  - Assembly version updates (.NET, Node.js)
  - Complete versioning example

Updated:
- sidebars.ts: Added Best Practices section between Build Types and CI Examples
  with all 5 new documentation pages properly linked

All documentation follows established patterns:
- Proper frontmatter with title and description
- Quick Start section with basic examples
- Complete working examples with full psakefile.ps1 code
- Multiple patterns and approaches
- Cross-references to related documentation
- "See Also" sections for navigation
- Comprehensive, production-ready code samples

Author: claude

docs/best-practices/_category_.json

@@ -0,0 +1,8 @@
+{
+  "label": "Best Practices",
+  "position": 4,
+  "link": {
+    "type": "generated-index",
+    "description": "Best practices for organizing, testing, and maintaining psake build scripts in production environments."
+  }
+}