Similarly to view builder, view building worker needs to be drained
in `storage_service::do_drain()`.
Storage service drain is happening at the same beginning of shutdown
procedure. Before this patch, the worker was still building views
after the storage service was drained and this caused errors like:
`Error applying view update to (named_gate_closed_exception)` and
`locator::no_such_tablet_map`.
Fixesscylladb/scylladb#25908Closesscylladb/scylladb#25984