scylla-cql-optimization.3.0.template: singlestat function should return single value

(cherry picked from commit 4270315)

Author: amnonh

grafana/scylla-cql-optimization.3.0.template.json

@@ -185,7 +185,7 @@
                         "description": "Scylla uses a shared-nothing model that shards all requests onto individual cores.\n\nScylla runs one application thread-per-core, and depends on explicit message passing, not shared memory between threads. This design avoids slow, unscalable lock primitives and cache bounces.\n\nIdeally, each request to a Scylla node reaches the right core (shard), avoiding internal communication between cores. This is not always the case, for example, when using a non-shard-aware Scylla driver (see more here: https://docs.scylladb.com/getting-started/scylla_drivers/)",
                         "targets": [
                             {
-                                "expr": "floor(100*sum(irate(scylla_storage_proxy_replica_cross_shard_ops{instance=~\"[[node]]\",cluster=~\"$cluster|$^\", dc=~\"$dc\", shard=~\"[[shard]]\"}[30s])) by ([[by]])/(sum(irate(scylla_storage_proxy_coordinator_reads_local_node{instance=~\"[[node]]\",cluster=~\"$cluster|$^\", dc=~\"$dc\", shard=~\"[[shard]]\"}[30s])) by ([[by]]) + sum(irate(scylla_storage_proxy_coordinator_total_write_attempts_local_node{instance=~\"[[node]]\",cluster=~\"$cluster|$^\", dc=~\"$dc\", shard=~\"[[shard]]\"}[30s])) by ([[by]])))",
+                                "expr": "floor(100*sum(irate(scylla_storage_proxy_replica_cross_shard_ops{instance=~\"[[node]]\",cluster=~\"$cluster|$^\", dc=~\"$dc\", shard=~\"[[shard]]\"}[30s]))/(sum(irate(scylla_storage_proxy_coordinator_reads_local_node{instance=~\"[[node]]\",cluster=~\"$cluster|$^\", dc=~\"$dc\", shard=~\"[[shard]]\"}[30s])) + sum(irate(scylla_storage_proxy_coordinator_total_write_attempts_local_node{instance=~\"[[node]]\",cluster=~\"$cluster|$^\", dc=~\"$dc\", shard=~\"[[shard]]\"}[30s]))))",
                                 "format": "time_series",
                                 "hide": false,
                                 "intervalFactor": 1,