Table with vector index should be updatable

[azevaykin]

Right now a table with a vector index is not updatable. And the message is confusing.

Status: INTERNAL_ERROR
Issues: 
<main>: Fatal: Optimization, code: 1070
    <main>:1:244: Fatal: ydb/core/kqp/provider/yql_kikimr_opt_build.cpp:215  AddUpdateOpToQueryBlock(): requirement indexTables.size() == 1 failed, message: Only index with one impl table is supported, code: 1

Table should be updatable. But vector index sees only current rows. To see new inserted rows a new vector index should be built.