feat: Add command to generate Metaflow debug configuration

[Sakshii-27]

This PR addresses issue #6 by making it significantly easier for users to debug Metaflow steps directly within VS Code without needing to manually hunt down the correct launch.json configuration.

As mentioned in the issue, users often struggle with Metaflow debugging because they don't realize they need "subProcess": true and "args": ["run", "--max-workers", "1"].

To solve this smoothly, I implemented a two-part approach:

1. Explicit Command (extension.generateDebugConfig): Adds a Metaflow: Generate Debug Config command to the palette. It intelligently checks for a .vscode/launch.json file in the workspace and safely pushes the perfect Metaflow Debug object to the configurations array.
2. Native Tooling (DebugConfigurationProvider): Hooked into vscode.debug.registerDebugConfigurationProvider. If a user manually clicks "Add Configuration..." inside the native Run and Debug view, VS Code will proactively offer the "Metaflow Debug" template in their dropdown menu and dynamically inject the snippet.

Related Issues

Fixes #6

Testing

• Tested locally using the Extension Development Host.
• Confirmed that running Metaflow: Generate Debug Config correctly creates launch.json if it doesn't exist, and safely appends to configurations if it does.
• Verified that "Metaflow Debug" shows up natively in the VS Code launch configuration dropdown.

Visual Proof

1. The Command Palette Option:

2. The Successfully Generated Configuration: