docs: enhance middleware documentation with advanced examples and bes…

[kunal-10-cloud]

Added comprehensive middleware examples including:

• Rate limiting middleware with token bucket algorithm
• JWT authentication middleware with custom claims
• Security headers middleware for web protection
• Request validation middleware with configurable rules
• Enhanced logging middleware with request/response capture
• Timeout middleware for request timeout enforcement

Expanded documentation sections:

• Detailed UseMiddleware section with clear explanations
• New UseMiddlewareWithContainer section for container access
• Comprehensive best practices guide covering:
  • Middleware ordering and execution flow
  • Error handling strategies
  • Performance considerations
  • Security best practices
  • Testing middleware in isolation

All examples are production-ready with proper error handling, thread safety where applicable, and follow GoFr conventions.

Documentation grew from 70 to 705 lines with detailed explanations and runnable code examples.

Fixes #1975

Pull Request Template

Description:

• Provide a concise explanation of the changes made.
• Mention the issue number(s) this PR addresses (if applicable).
• Highlight the motivation behind the changes and the expected benefits.