[Feature Request]: Add `MENTIONS` relationship in Nebula Property Graph Store

[douglasrfaisal-gl]

Feature Description

Add MENTIONS relationship when upserting nodes to Nebula Property Graph Store.

Reason

We are developing a function for deleting parts of the graph based on the chunk IDs. The function is already working in Neo4j, but it's not working in Nebula Graph due to no relationships between chunks and entities.

Value of Feature

This is useful for tracing which chunks mention a certain entity, and I believe this has already been implemented in Neo4j, but not in Nebula Graph yet.

Here's the schema produced by using the PropertyGraphIndex on Nebula Graph. I expect there is a relation from Chunk to Entity.

Here is an example when using Neo4j. I can find similar chunks that refer to the same entities