Enhances Git learning resources

[jjsilva4]

Fixes #

Proposed Changes

• Adds a new "Foundations of Git" certification course, offering a structured learning path for new Git users.
• Updates the "How to learn Git" guide to clearly present the certification course and the existing YouTube playlist as distinct learning options.
• Revises guide summaries to reflect the inclusion of the new Git foundations course and expanded learning resources.
• Bumps documentation last_verified and Last updated dates to April 2026.