fix: bigtable - avoid instance recreation due to node_scaling_factor addition in 6.34.0 for existing clusters (#13902) (#22674)

[upstream:bc107b1cc3314d2efadb459e69a4db7ac501503a]

Signed-off-by: Modular Magician <magic-modules@google.com>

Author: modular-magician

.changelog/13902.txt

@@ -0,0 +1,3 @@
+```release-note:bug
+bigtable: fixed forced instance recreation due to addition of `cluster.node_scaling_factor` for `google_bigtable_instance` in 6.34.0
+```

google/services/bigtable/resource_bigtable_instance.go

@@ -537,6 +537,8 @@ func flattenBigtableCluster(c *bigtable.ClusterInfo) map[string]interface{} {
 		nodeScalingFactor = "NodeScalingFactor1X"
 	case bigtable.NodeScalingFactor2X:
 		nodeScalingFactor = "NodeScalingFactor2X"
+	default:
+		nodeScalingFactor = "NodeScalingFactor1X"
 	}
 
 	cluster := map[string]interface{}{

google/services/bigtable/resource_bigtable_instance_internal_test.go

@@ -169,8 +169,8 @@ func TestUnitBigtable_flattenBigtableCluster(t *testing.T) {
 						"storage_target": 60,
 					},
 				},
-				// unspecified node scaling factor in input will lead to an empty string here
-				"node_scaling_factor": "",
+				// unspecified node scaling factor in input will default to 1X
+				"node_scaling_factor": "NodeScalingFactor1X",
 			},
 		},
 		"HDD manual scaling": {