Implement new structure for Git documentation

Reorganize our Git documentation to improve the user experience by separating GitLab UI and Git CLI tasks.

The scope of this issue is the Learn Git section inside Use GitLab, and not Tutorials: Learn Git.

This issue outlines the plan to implement the proposed changes. These include:

• Rename Learn Git to Use Git ✅
• Create parent sections and add content ✅
• Create child pages, move, and update Git-related content ✅
• Update Learn Git page table ✅

Proposed navigation changes

- Use Git
  - Getting started
    - Install Git
    - Common Git commands
    - Tutorial: Create your first commit
  - Basic operations
     - Create a project
     - Clone a repository
     - Create a branch
     - Stage, commit, and push changes
     - Stash changes
     - Create a merge request
     - Add files to a branch
     - Merge your branch
     - Update a fork
  - Advanced operations
     - Rebase and resolve conflicts
     - Cherry pick changes
     - Revert and undo changes
     - Reduce repository size
     - File management
     - Tutorial: Update Git remote URLs
  - Troubleshooting

Related issues

• #472128 (closed)