Update tidb-resource-control-background-tasks (pingcap#22052)

Author: Frank945946

tidb-resource-control-background-tasks.md

@@ -28,7 +28,7 @@ TiDB supports the following types of background tasks:
 
 <CustomContent platform="tidb">
 
-- `lightning`: perform import tasks using [TiDB Lightning](/tidb-lightning/tidb-lightning-overview.md). Both physical and logical import modes of TiDB Lightning are supported.
+- `lightning`: perform import tasks using [TiDB Lightning](/tidb-lightning/tidb-lightning-overview.md) or [`IMPORT INTO`](/sql-statements/sql-statement-import-into.md). Both TiDB Lightning physical and logical import modes are supported.
 - `br`: perform backup and restore tasks using [BR](/br/backup-and-restore-overview.md). PITR is not supported.
 - `ddl`: control the resource usage during the batch data write back phase of Reorg DDLs.
 - `stats`: the [collect statistics](/statistics.md#collect-statistics) tasks that are manually executed or automatically triggered by TiDB.