[Fix] Move Spark Version selector defaults to Terraform

Move defaults for `databricks_spark_version` data source from Go SDK to the
Terraform. First part of #5218 work - after new Go SDK is merged, we'll need to change
Scala default to `2.1`.

Related to databricks/databricks-sdk-go#1331

Author: alexott

NEXT_CHANGELOG.md

@@ -12,6 +12,7 @@
 ### Bug Fixes
 
 * Fix spurious plan diffs in `databricks_model_serving` and `databricks_model_serving_provisioned_throughput` resources due to tag reordering ([#5120](https://github.com/databricks/terraform-provider-databricks/pull/5120))
+* Move Spark Version selector defaults to Terraform ([#5219](https://github.com/databricks/terraform-provider-databricks/pull/5219)).
 
 ### Documentation
 

clusters/data_spark_version.go

@@ -27,6 +27,9 @@ func DataSourceSparkVersion() common.Resource {
 	}, func(s map[string]*schema.Schema) map[string]*schema.Schema {
 		common.CustomizeSchemaPath(s, "photon").SetDeprecated("Specify runtime_engine=\"PHOTON\" in the cluster configuration")
 		common.CustomizeSchemaPath(s, "graviton").SetDeprecated("Not required anymore - it's automatically enabled on the Graviton-based node types")
+		common.CustomizeSchemaPath(s, "scala").SetDefault("2.12")
+		common.CustomizeSchemaPath(s, "latest").SetDefault(true)
+
 		common.NamespaceCustomizeSchemaMap(s)
 		return s
 	})