Allow LowCardinality strings for ngrambf_v1/tokenbf_v1 indexes

Why it matters

This feature enables more efficient indexing and query performance optimization for LowCardinality string columns by allowing the use of ngrambf_v1 and tokenbf_v1 index types, which were previously unsupported for such columns.

How to use it

Users can create or alter tables to add ngrambf_v1 or tokenbf_v1 indexes on columns with the LowCardinality(String) type as usual. No additional configuration is required beyond specifying these index types on the applicable LowCardinality string columns.