Improve search index eviction (#111542)

* Modify index eviction mechanism such that unowned indexes are also evicted.

* Propagate OwnsIndex function to bleve backend

Fix tests.

Stop eviction goroutine when stopping backend.

Make linter happy.

Make sure we stop backend created by tests.

Review suggestion.

Removed newline.

pkg/storage/unified/resource/search_server_distributor.go

@@ -90,8 +90,6 @@ var (
 	searchRingRead = ring.NewOp([]ring.InstanceState{ring.ACTIVE}, func(s ring.InstanceState) bool {
 		return s != ring.ACTIVE
 	})
-	// operation used by the search-servers to check if they own the namespace
-	searchOwnerRead = ring.NewOp([]ring.InstanceState{ring.JOINING, ring.ACTIVE, ring.LEAVING}, nil)
 )
 
 func (ds *distributorServer) Search(ctx context.Context, r *resourcepb.ResourceSearchRequest) (*resourcepb.ResourceSearchResponse, error) {