feat: add graphrag modes

[taprosoft]

Description

• Improve async LLM call of LightRAG and NanoGraphRAG to reduce indexing time
• Add global, local, hybrid search mode support in LightRAG & NanoGraphRAG
• Add UI settings to customize LightRAG & NanoGraphRAG prompts
• Fix Custom Entity Extract Prompt for GraphRag or LightRag #567 [REQUEST] added setting for lightrag retrieval #502

Type of change

• New features (non-breaking change).
• Bug fix (non-breaking change).
• Breaking change (fix or feature that would cause existing functionality not to work as expected).

Checklist

• I have performed a self-review of my code.
• I have added thorough tests if it is a core feature.
• There is a reference to the original bug report and related work.
• I have commented on my code, particularly in hard-to-understand areas.
• The feature is well documented.