[Features]Make the GraphIndex entity extraction prompt configurable

[earayu]

Currently, the prompt for entity relationship extraction in GraphIndex is hardcoded within the system.

To allow for greater flexibility and customization, this prompt should be configurable by the user. This would enable users to tailor the extraction process to their specific needs and domains.

[github-actions]

This issue has been marked as stale because it has been open for 30 days with no activity