[FEAT] Display LLM generated summary on sample data from discover

[chishui]

Is your feature request related to a problem? Please describe.
As part of query assist feature, in discover page, it is great if we could generate a data summary to provide useful insights on PPL query and on the data queried from it.

Describe the solution you'd like

1. Sending sample data from discover page to LLM and let it generate a summary on data.
2. Display a summary panel when query assist feature is enabled.

Describe alternatives you've considered
N/A

Additional context
N/A