Vector search related implementation moved to a new module vector_search.
As the vector search functionality is going to be extended, it is better to keep it in a separate module.
The DNS resolution logic and its background task are moved out of the `vector_store_client` and into a new, dedicated class `vector_search::dns`.
This refactoring is the first step towards supporting DNS hostnames that resolve to multiple IP addresses.
References: VECTOR-187
No backport needed as this is refactoring.
Closesscylladb/scylladb#26052
* github.com:scylladb/scylladb:
vector_store_client_test: Verify DNS is not refreshed when disabled
vector_store_client: Extract DNS logic into a dedicated class
vector_search: Apply clang-format
vector_store_client: Move to vector_search module
b205e1a3da