make executors self-contained, remove redundant pre-filter

[NOTICKET][doc] remove column filter and fallback cap for full-schema approach

[NOTICKET][db] add sheet-level retrieval and focus LLM schema context to retrieved columns

[NOTICKET][doc] fix aggregate count operation when value_col is not specified

fix: 5 bug fixes on tabular executor

[KM-515][document] Make Query for Tabular Type (XLSX & CSV)

[KM-512] add Pydantic model the LLM fills via function calling in sql_query, and add same signature for db and tabular

[KM-512] create folder for querying from bd/tabular docs