Update Lucene index and documentation

[fh-ms]

### Summary
This pull request introduces updates and enhancements to the Lucene index system.

### Changes
- Updated Lucene documentation, including persistence details.
- Introduced a specialized type handler for Lucene indexing.
- Added a new in-memory `GraphDirectory` implementation for Lucene index.
- Refactored existing code to improve clarity and maintainability.
- Updated and extended test coverage to ensure correctness.
- Included Javadoc for relevant components to improve developer understanding.