feat(order): enhance layout and integrate Mpesa payment processing

[muruthigitau]

✅ Summary of Enhancements:

💳 Mpesa Payment Integration:

• Updated order.html layout:
  • Added phone number input field for Mpesa
  • Introduced payment method selection
  • Modified payment button logic to support Mpesa payments
    [order.html](https://github.com/frappe/webshop/pull/288/files#diff-7873531d03d5dc23ead5d129703cc1e0612d2f4142dc538ff3997ed6c9fa3a82L37-R42)

📜 JavaScript Refactor:

• Refactored order.js to:
  • Initialize elements cleanly
  • Set up event listeners
  • Add helper functions to streamline Mpesa payment logic
    [order.js](https://github.com/frappe/webshop/pull/288/files#diff-4719e0a9f2d4c138fd1916b67c28eac47fc4ab367b7d71ae39c00d28cfcfd9cbL5-R180)

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🖼️ Screenshots of UI Changes:

1. Payment Method Option and Phone Number Input