[Enhencement](Export) add property for outfile/export and add test (#18997)

This pr does three things:
1. add `delete_existing_files` property for outfile/export. If `delete_existing_files = true`, export/outfile will delete all files under file_path first.
2. add p2 test for export
3. modify docs

fe/fe-core/src/main/java/org/apache/doris/analysis/ExportStmt.java

@@ -81,6 +81,7 @@ public class ExportStmt extends StatementBase {
     private String label;
 
     private String maxFileSize;
+    private String deleteExistingFiles;
     private SessionVariable sessionVariables;
 
     private String qualifiedUser;
@@ -338,6 +339,7 @@ public class ExportStmt extends StatementBase {
 
         // max_file_size
         this.maxFileSize = properties.getOrDefault(OutFileClause.PROP_MAX_FILE_SIZE, "");
+        this.deleteExistingFiles = properties.getOrDefault(OutFileClause.PROP_DELETE_EXISTING_FILES, "");
 
         if (properties.containsKey(LABEL)) {
             FeNameFormat.checkLabel(properties.get(LABEL));
@@ -397,4 +399,8 @@ public class ExportStmt extends StatementBase {
     public String getMaxFileSize() {
         return maxFileSize;
     }
+
+    public String getDeleteExistingFiles() {
+        return deleteExistingFiles;
+    }
 }

fe/fe-core/src/main/java/org/apache/doris/analysis/OutFileClause.java

@@ -130,8 +130,8 @@ public class OutFileClause {
     public static final String PROP_LINE_DELIMITER = "line_delimiter";
     public static final String PROP_MAX_FILE_SIZE = "max_file_size";
     private static final String PROP_SUCCESS_FILE_NAME = "success_file_name";
+    public static final String PROP_DELETE_EXISTING_FILES = "delete_existing_files";
     private static final String PARQUET_PROP_PREFIX = "parquet.";
-    private static final String ORC_PROP_PREFIX = "orc.";
     private static final String SCHEMA = "schema";
 
     private static final long DEFAULT_MAX_FILE_SIZE_BYTES = 1 * 1024 * 1024 * 1024; // 1GB
@@ -148,6 +148,7 @@ public class OutFileClause {
     private String lineDelimiter = "\n";
     private TFileFormatType fileFormatType;
     private long maxFileSizeBytes = DEFAULT_MAX_FILE_SIZE_BYTES;
+    private boolean deleteExistingFiles = false;
     private BrokerDesc brokerDesc = null;
     // True if result is written to local disk.
     // If set to true, the brokerDesc must be null.
@@ -597,6 +598,12 @@ public class OutFileClause {
             processedPropKeys.add(PROP_MAX_FILE_SIZE);
         }
 
+        if (properties.containsKey(PROP_DELETE_EXISTING_FILES)) {
+            deleteExistingFiles = Boolean.parseBoolean(properties.get(PROP_DELETE_EXISTING_FILES))
+                                    & Config.enable_delete_existing_files;
+            processedPropKeys.add(PROP_DELETE_EXISTING_FILES);
+        }
+
         if (properties.containsKey(PROP_SUCCESS_FILE_NAME)) {
             successFileName = properties.get(PROP_SUCCESS_FILE_NAME);
             FeNameFormat.checkCommonName("file name", successFileName);
@@ -833,6 +840,7 @@ public class OutFileClause {
             sinkOptions.setLineDelimiter(lineDelimiter);
         }
         sinkOptions.setMaxFileSizeBytes(maxFileSizeBytes);
+        sinkOptions.setDeleteExistingFiles(deleteExistingFiles);
         if (brokerDesc != null) {
             sinkOptions.setBrokerProperties(brokerDesc.getProperties());
             // broker_addresses of sinkOptions will be set in Coordinator.

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

@@ -143,6 +143,8 @@ public class ExportJob implements Writable {
     private int timeoutSecond;
     @SerializedName("maxFileSize")
     private String maxFileSize;
+    @SerializedName("deleteExistingFiles")
+    private String deleteExistingFiles;
     // progress has two functions at EXPORTING stage:
     // 1. when progress < 100, it indicates exporting
     // 2. set progress = 100 ONLY when exporting progress is completely done
@@ -222,6 +224,7 @@ public class ExportJob implements Writable {
         this.userIdentity = stmt.getUserIdentity();
         this.format = stmt.getFormat();
         this.maxFileSize = stmt.getMaxFileSize();
+        this.deleteExistingFiles = stmt.getDeleteExistingFiles();
         this.partitions = stmt.getPartitions();
 
         this.exportTable = db.getTableOrDdlException(stmt.getTblName().getTbl());
@@ -287,6 +290,9 @@ public class ExportJob implements Writable {
         if (!maxFileSize.isEmpty()) {
             outfileProperties.put(OutFileClause.PROP_MAX_FILE_SIZE, maxFileSize);
         }
+        if (!deleteExistingFiles.isEmpty()) {
+            outfileProperties.put(OutFileClause.PROP_DELETE_EXISTING_FILES, deleteExistingFiles);
+        }
 
         // broker properties
         // outfile clause's broker properties need 'broker.' prefix
@@ -359,6 +365,10 @@ public class ExportJob implements Writable {
         return maxFileSize;
     }
 
+    public String getDeleteExistingFiles() {
+        return deleteExistingFiles;
+    }
+
     public String getQualifiedUser() {
         return qualifiedUser;
     }

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

@@ -420,6 +420,7 @@ public class ExportMgr extends MasterDaemon {
         infoMap.put("columns", job.getColumns());
         infoMap.put("tablet_num", job.getTabletLocations() == null ? -1 : job.getTabletLocations().size());
         infoMap.put("max_file_size", job.getMaxFileSize());
+        infoMap.put("delete_existing_files", job.getDeleteExistingFiles());
         jobInfo.add(new Gson().toJson(infoMap));
         // path
         jobInfo.add(job.getExportPath());