read env var only once (#2899)

Author: lantoli

internal/config/advanced_cluster_v2_schema.go

@@ -8,7 +8,9 @@ import (
 const AdvancedClusterV2SchemaEnvVar = "MONGODB_ATLAS_ADVANCED_CLUSTER_V2_SCHEMA"
 const allowAdvancedClusterV2Schema = false // Don't allow in master branch yet, not in const block to allow automatic change
 
+// Environment variable is read only once to avoid possible changes during runtime
+var advancedClusterV2Schema, _ = strconv.ParseBool(os.Getenv(AdvancedClusterV2SchemaEnvVar))
+
 func AdvancedClusterV2Schema() bool {
-	env, _ := strconv.ParseBool(os.Getenv(AdvancedClusterV2SchemaEnvVar))
-	return allowAdvancedClusterV2Schema && env
+	return allowAdvancedClusterV2Schema && advancedClusterV2Schema
 }