Re-design out-dated Guide pages

Created by: zlonko

The following pages should be refactored into our new Guide layout design:

• guides/dev-onboarding-how-is-it-unique #5231 (closed) **
• guides/continuous-developer-onboarding #5240 **

This issue anticipates making layout changes to these pages to ensure consistency across the Guide pages.

1. Brand should first re-design these pages to conform them to our new design standards: here.
2. Then developers should implement, changing these pages using the WebinarAndGuideLayout.tsx component.