PLT-6355: Use separate Read Replicas for Search. (#6216)

config/config.json

@@ -73,6 +73,7 @@
         "DriverName": "mysql",
         "DataSource": "mmuser:mostest@tcp(dockerhost:3306)/mattermost_test?charset=utf8mb4,utf8&readTimeout=30s&writeTimeout=30s",
         "DataSourceReplicas": [],
+        "DataSourceSearchReplicas": [],
         "MaxIdleConns": 20,
         "MaxOpenConns": 300,
         "Trace": false,