[fix](Export) fix a memory leak in the FE because of the ExportJob (#…

…44019)

### What problem does this PR solve?

Problem Summary:
When an `Export` job has finished or been cancelled, `ExportMgr` will
maintain a reference of the `ExportJob` object. Therefore, we need to
clear these no longer used objects; otherwise it will cause a memory
leak in the FE.

fe/fe-core/src/main/java/org/apache/doris/load/ExportJob.java

@@ -703,6 +703,9 @@ private void cancelExportJobUnprotected(ExportFailMsg.CancelType type, String ms
         finishTimeMs = System.currentTimeMillis();
         failMsg = new ExportFailMsg(type, msg);
         jobExecutorList.clear();
+        selectStmtListPerParallel.clear();
+        allOutfileInfo.clear();
+        partitionToVersion.clear();
         if (FeConstants.runningUnitTest) {
             return;
         }
@@ -750,6 +753,9 @@ private void finishExportJobUnprotected() {
         outfileInfo = GsonUtils.GSON.toJson(allOutfileInfo);
         // Clear the jobExecutorList to release memory.
         jobExecutorList.clear();
+        selectStmtListPerParallel.clear();
+        allOutfileInfo.clear();
+        partitionToVersion.clear();
         Env.getCurrentEnv().getEditLog().logExportUpdateState(this, ExportJobState.FINISHED);
         LOG.info("finish export job {}", id);
     }