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3589a135 - community: make `SET allow_experimental_[engine]_index` configurabe in vectorstores.clickhouse (#18107)

community: make `SET allow_experimental_[engine]_index` configurabe in vectorstores.clickhouse (#18107) ## Description & Issue While following the official doc to use clickhouse as a vectorstore, I found only the default `annoy` index is properly supported. But I want to try another engine `usearch` for `annoy` is not properly supported on ARM platforms. Here is the settings I prefer: ``` python settings = ClickhouseSettings( table="wiki_Ethereum", index_type="usearch", # annoy by default index_param=[], ) ``` The above settings do not work for the command `set allow_experimental_annoy_index=1` is hard-coded. This PR will make sure the experimental feature follow the `index_type` which is also consistent with Clickhouse's naming conventions.