Add GitHub Copilot CLI challenges and update documentation

[tcardosoMSFT]

New Challenge Content:

• Added Challenge 08: Getting Started with GitHub Copilot in the CLI, with detailed student instructions (Student/Challenge-08.md) and a comprehensive coach's guide (Coach/Solution-08.md). This covers installing the CLI extension, using gh copilot suggest and gh copilot explain, and exploring iterative refinement in the terminal. [1] [2]
• Added Challenge 09: Automating DevOps Workflows with GitHub Copilot CLI, including a student challenge (Student/Challenge-09.md) and a coach's guide (Coach/Solution-09.md). This guides users through a realistic DevOps workflow automated via Copilot CLI, from repo setup to release management and operational tasks. [1] [2]

Documentation and Navigation Updates:

• Updated both the main README (README.md) and the coach's guide (Coach/README.md) to add Challenges 08 and 09 to the challenge list, update prerequisites to include GitHub CLI, and adjust the recommended timing for each challenge. [1] [2] [3]
• Enhanced navigation links in student and coach challenge files for smoother progression between challenges (e.g., adding "Next Challenge" and "Previous Challenge" links). [1] [2]

These changes provide a more comprehensive learning path, enabling students to gain hands-on experience with Copilot beyond the IDE and into practical DevOps automation.

References: [1] [2] [3] [4] [5] [6] [7] [8] [9]