Add collection-aware scenario discovery and creation

[cidrblock]

Enable Native Collection Support Through Auto-Detection

This PR enables Molecule to operate natively from Ansible collection roots by automatically detecting collections and encouraging proper scenario placement.

How It Works

When executed from a collection root (directory containing galaxy.yml with required name and namespace fields), Molecule now:

• Automatically detects the collection and logs the detected collection name
• Encourages best practices by defaulting to search for scenarios in extensions/molecule/*/molecule.yml
• Supports legacy setups with a migration warning when molecule/ exists in the collection root
• Respects user overrides via the MOLECULE_GLOB environment variable

Behavior Details

1. Environment Override: If MOLECULE_GLOB is set, that pattern is used (highest priority)

2. No Collection: If no valid galaxy.yml is found, use standard molecule/*/molecule.yml pattern

3. Legacy Collection: If collection detected AND molecule/ directory exists in root:

   • Warns: "Molecule scenarios should migrate to 'extensions/molecule'"
   • Uses standard molecule/*/molecule.yml pattern for backward compatibility

4. Modern Collection: If collection detected but no molecule/ in root:

   • Logs: "Collection 'namespace.name' detected"
   • Logs: "Scenarios will be used from 'extensions/molecule'"
   • Uses collection pattern: extensions/molecule/*/molecule.yml

Benefits

• Zero Configuration: Works automatically when galaxy.yml is present
• Backward Compatible: Existing collections with molecule/ in root continue working
• Encourages Best Practices: Guides users toward the recommended extensions/molecule/ structure
• Clear Migration Path: Provides helpful warnings for legacy setups
• User Control: Can be overridden via environment variable if needed

Example Usage

# In a collection root with extensions/molecule/ structure
$ molecule test
INFO Collection 'community.general' detected
INFO Scenarios will be used from 'extensions/molecule'

# In a collection root with legacy molecule/ structure  
$ molecule test
WARNING Molecule scenarios should migrate to 'extensions/molecule'
# Uses molecule/*/molecule.yml for compatibility

Files Changed

• Core Logic: src/molecule/util.py - Implements the auto-detection algorithm
• Integration: Various command files updated to use the new detection
• Tests: Updated unit and integration tests to match new behavior
• Sample Structure: Moved test collection to proper extensions/molecule/ layout

This change makes Molecule collection-aware by default while maintaining full backward compatibility and providing clear guidance for modernization.