### What problem does this PR solve?

#9082 #6365

<u> **WARNING: it's not compatible with the older version of `Agent`
module, which means that `Agent` from older versions can not work
anymore.**</u>

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

### What problem does this PR solve?

More robust MCP tool call conn.

### Type of change

- [x] Refactoring

### What problem does this PR solve?

Change mcp_client module to rag/utils/conn.

### Type of change

- [x] Refactoring

### What problem does this PR solve?

Add MCP dashboard functionalities list_tools and test_tool.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

### What problem does this PR solve?

This is a cherry-pick from #7781 as requested.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>