fix: add prql description

[ncuwaln]

I hereby agree to the terms of the CLA available at: https://docs.databend.com/dev/policies/cla/

Summary

fix sql_dialect description info

• Fixes Feature: prql dialect support #14811

Tests

• Unit Test
• Logic Test
• Benchmark Test
• No Test - just add a setting description

Type of change

• Bug Fix (non-breaking change which fixes an issue)
• New Feature (non-breaking change which adds functionality)
• Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• Documentation Update
• Refactoring
• Performance Improvement
• Other (please describe):

[BohuTANG]

Thanks for your contribution!