Design: Search DSL

### What would you like to be added?

Design the Search DSL.

### Why is this needed?

Considering the low learning cost of SQL for developers, only the SQL search method is supported in Karpor v0.4.0. However, in some search scenarios, providing specialized DSLs will simplify the search and improve the experience.

Start by reviewing the existing SQL search method referenced in the issue and how search scenarios are currently represented. The issue names no files or tests, so the first step is to identify the relevant search entry points and establish the Search DSL's scope and requirements. Done means an agreed design that improves search usability without relying only on SQL.

Written by the indexing model from the issue text.