[Improvement]Remove Nebula Graph support from Aperag #1400
Description
Background
Aperag currently supports Nebula Graph as one of its graph storage backends.
Proposal
Remove Nebula Graph integration from Aperag, including:
- Remove Nebula-specific connector and adapter code
- Update documentation to reflect supported storage backends
- Provide migration guide for existing users currently using Nebula Graph
- Update configuration files and examples
- Clean up related dependencies and tests
This change will help streamline the codebase and focus development efforts on the remaining supported storage solutions.